| CommandLine 2.0 Library Manual | -
Written by Chris Lattner
-
+
Written by Chris Lattner
+| -Introduction - |
This document describes the CommandLine argument processing library. It will show you how to use it, and what it can do. The CommandLine library uses a declarative approach to specifying the command line options that your program takes. By default, these options declarations implicitly hold the value parsed for the option declared (of course this can be -changed).
+changed).
-Although there are a lot of command line argument parsing libraries out -there in many different languages, none of them fit well with what I needed. By -looking at the features and problems of other libraries, I designed the -CommandLine library to have the following features:+
Although there are a lot of command line argument parsing libraries +out there in many different languages, none of them fit well with what I needed. +By looking at the features and problems of other libraries, I designed the +CommandLine library to have the following features:
+argument values are captured transparently into user defined global variables, +which can be accessed like any other variable (and with the same +performance).
+error prone constructs, it also leads to dramatically cleaner source code.
+parser. This means that you don't have to write any boilerplate +code.
+loaded options trivial.
+assigned a value that is not valid for your enum type.
+arguments. This is possible because CommandLine is...
+you declare it. Custom parsers are no problem.
+tool. Additionally, it does most of the basic correctness checking for +you.
+href="#cl::ConsumeAfter">interpreter style options.
- +
This document will hopefully let you jump in and start using CommandLine in +your utility quickly and painlessly. Additionally it should be a simple +reference manual to figure out how stuff works. If it is failing in some area +(or you want an extension to the library), nag the author, Chris Lattner.
+| -Quick Start Guide - |
This section of the manual runs through a simple CommandLine'ification of a basic compiler tool. This is intended to show you how to jump into using the CommandLine library in your own program, and show you some of the cool things it -can do.
+can do.
-To start out, you need to include the CommandLine header file into your -program:+
To start out, you need to include the CommandLine header file into your +program:
#include "Support/CommandLine.h" -
+ -Additionally, you need to add this as the first line of your main program:
+
Additionally, you need to add this as the first line of your main +program:
int main(int argc, char **argv) {
- cl::ParseCommandLineOptions(argc, argv);
+ cl::ParseCommandLineOptions(argc, argv);
...
}
-+ -... which actually parses the arguments and fills in the variable -declarations.
+
... which actually parses the arguments and fills in the variable +declarations.
-Now that you are ready to support command line arguments, we need to tell the +Now that you are ready to support command line arguments, we need to tell the system which ones we want, and what type of argument they are. The CommandLine -library uses a declarative syntax to model cammand line arguments with the -variable declarations that capture the parsed values. This means that for every -command line option that you would like to support, there should be a variable -declaration to capture the result. For example, in a compiler, we would like to -support the unix standard '-o <filename>' option to specify where -to put the output. With the CommandLine library, this is represented like -this:
- -
-cl::opt<string> OutputFilename("o", cl::desc("Specify output filename"), cl::value_desc("filename")); -
- -This declares a variable "OutputFilename" that is used to capture the -result of the "o" argument (first parameter). We specify that this is -a simple scalar option by using the "cl::opt" -template (as opposed to the "cl::list -template), and tell the CommandLine library that the data type that we are -parsing is a string.
- -The second and third parameters (which are optional) are used to specify what to -output for the "--help" option. In this case, we get a line that looks -like this:
+library uses a declarative syntax to model command line arguments with the +global variable declarations that capture the parsed values. This means that +for every command line option that you would like to support, there should be a +global variable declaration to capture the result. For example, in a compiler, +we would like to support the unix standard '-o <filename>' option +to specify where to put the output. With the CommandLine library, this is +represented like this:
+ ++ +cl::opt<string> OutputFilename("o", cl::desc("Specify output filename"), cl::value_desc("filename")); +
+ +This declares a global variable "OutputFilename" that is used to +capture the result of the "o" argument (first parameter). We specify +that this is a simple scalar option by using the "cl::opt" template (as opposed to the "cl::list template), and tell the CommandLine library +that the data type that we are parsing is a string.
+ +The second and third parameters (which are optional) are used to specify what +to output for the "--help" option. In this case, we get a line that +looks like this:
USAGE: compiler [options] OPTIONS: -help - display available options (--help-hidden for more) - -o <filename> - Specify output filename + -o <filename> - Specify output filename-Because we specified that the command line option should parse using the +
Because we specified that the command line option should parse using the string data type, the variable declared is automatically usable as a real string in all contexts that a normal C++ string object may be used. For -example:
+example:
... ofstream Output(OutputFilename.c_str()); if (Out.good()) ... ... -
+ -There are many different options that you can use to customize the command line -option handling library, but the above example shows the general interface to -these options. The options can be specified in any order, and are specified +
There are many different options that you can use to customize the command +line option handling library, but the above example shows the general interface +to these options. The options can be specified in any order, and are specified with helper functions like cl::desc(...), so -there are no positional dependencies to have to remember. The available options -are discussed in detail in the Reference Guide.
- +there are no positional dependencies to remember. The available options are +discussed in detail in the Reference Guide.
-Continuing the example, we would like to have our compiler take an input +Continuing the example, we would like to have our compiler take an input filename as well as an output filename, but we do not want the input filename to be specified with a hyphen (ie, not -filename.c). To support this style of argument, the CommandLine library allows for positional arguments to be specified for the program. These positional arguments are filled with command line parameters that are not -in option form. We use this feature like this:
+in option form. We use this feature like this:
cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-"));-This declaration indicates that the first positional argument should be treated -as the input filename. Here we use the This declaration indicates that the first positional argument should be +treated as the input filename. Here we use the cl::init option to specify an initial value for the command line option, which is used if the option is not specified (if you do not specify a cl::init modifier for an option, then @@ -251,69 +279,73 @@ the default constructor for the data type is used to initialize the value). Command line options default to being optional, so if we would like to require that the user always specify an input filename, we would add the cl::Required flag, and we could eliminate the -cl::init modifier, like this:
+cl::init modifier, like this:
cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::Required);-Again, the CommandLine library does not require the options to be specified in -any particular order, so the above declaration is equivalent to:
+
Again, the CommandLine library does not require the options to be specified +in any particular order, so the above declaration is equivalent to:
cl::opt<string> InputFilename(cl::Positional, cl::Required, cl::desc("<input file>"));-By simply adding the cl::Required flag, the -CommandLine library will automatically issue an error if the argument is not +
By simply adding the cl::Required flag, +the CommandLine library will automatically issue an error if the argument is not specified, which shifts all of the command line option verification code out of your application into the library. This is just one example of how using flags can alter the default behaviour of the library, on a per-option basis. By adding one of the declarations above, the --help option synopsis is now -extended to:
+extended to:
-USAGE: compiler [options] <input file> +USAGE: compiler [options] <input file> OPTIONS: -help - display available options (--help-hidden for more) -o <filename> - Specify output filename-... indicating that an input filename is expected.
+
... indicating that an input filename is expected.
+| -Boolean Arguments - |
In addition to input and output filenames, we would like the compiler example +to support three boolean flags: "-f" to force overwriting of the output file, "--quiet" to enable quiet mode, and "-q" for backwards compatibility with some of our users. We can support these by declaring options -of boolean type like this:
+of boolean type like this:
cl::opt<bool> Force ("f", cl::desc("Overwrite output files")); cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); cl::opt<bool> Quiet2("q", cl::desc("Don't print informational messages"), cl::Hidden); -
+ -This does what you would expect: it declares three boolean variables +
This does what you would expect: it declares three boolean variables ("Force", "Quiet", and "Quiet2") to recognize these options. Note that the "-q" option is specified with the "cl::Hidden" flag. This modifier prevents it from being shown by the standard "--help" output (note that it is still -shown in the "--help-hidden" output).
+shown in the "--help-hidden" output).
-The CommandLine library uses a different parser for different data types. For -example, in the string case, the argument passed to the option is copied -literally into the content of the string variable... we obviously cannot do that -in the boolean case, however, so we must use a smarter parser. In the case of -the boolean parser, it allows no options (in which case it assigns the value of -true to the variable), or it allows the values "true" or -"false" to be specified, allowing any of the following inputs:+
The CommandLine library uses a different parser +for different data types. For example, in the string case, the argument passed +to the option is copied literally into the content of the string variable... we +obviously cannot do that in the boolean case, however, so we must use a smarter +parser. In the case of the boolean parser, it allows no options (in which case +it assigns the value of true to the variable), or it allows the values +"true" or "false" to be specified, allowing any of the +following inputs:
compiler -f # No value, 'Force' == true @@ -322,125 +354,133 @@ true to the variable), or it allows the values "true" or compiler -f=FALSE # Value specified, 'Force' == false-... you get the idea. The bool parser just turns the string values into boolean -values, and rejects things like 'compiler -f=foo'. Similarly, the -float, double, and int parsers work like you would expect, using the -'strtol' and 'strtod' C library calls to parse the string -value into the specified data type.
+
... you get the idea. The bool parser just turns +the string values into boolean values, and rejects things like 'compiler +-f=foo'. Similarly, the float, double, and int parsers work +like you would expect, using the 'strtol' and 'strtod' C +library calls to parse the string value into the specified data type.
-With the declarations above, "compiler --help" emits this:+
With the declarations above, "compiler --help" emits this:
USAGE: compiler [options] <input file> OPTIONS: - -f - Overwrite output files + -f - Overwrite output files -o - Override output filename - -quiet - Don't print informational messages + -quiet - Don't print informational messages -help - display available options (--help-hidden for more) -
+ -and "opt --help-hidden" prints this:
+
and "opt --help-hidden" prints this:
-USAGE: opt [options] <input file> +USAGE: compiler [options] <input file> OPTIONS: -f - Overwrite output files -o - Override output filename - -q - Don't print informational messages + -q - Don't print informational messages -quiet - Don't print informational messages -help - display available options (--help-hidden for more) -
+ -This brief example has shown you how to use the 'This brief example has shown you how to use the 'cl::opt' class to parse simple scalar command line arguments. In addition to simple scalar arguments, the CommandLine library also provides primitives to support CommandLine option aliases, -and lists of options.
+and lists of options.
+| -Argument Aliases - |
+
So far, the example works well, except for the fact that we need to check the +quiet condition like this now:
... if (!Quiet && !Quiet2) printInformationalMessage(...); ... -
+ -... which is a real pain! Instead of defining two values for the same +
... which is a real pain! Instead of defining two values for the same condition, we can use the "cl::alias" class to make the "-q" option an alias for the "-quiet" option, instead of providing -a value itself:
+a value itself:
cl::opt<bool> Force ("f", cl::desc("Overwrite output files")); cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); cl::alias QuietA("q", cl::desc("Alias for -quiet"), cl::aliasopt(Quiet)); -
+ -The third line (which is the only one we modified from above) defines a +
The third line (which is the only one we modified from above) defines a "-q alias that updates the "Quiet" variable (as specified by the cl::aliasopt modifier) whenever it is specified. Because aliases do not hold state, the only thing the program has to query is the Quiet variable now. Another nice feature of aliases is that they automatically hide themselves from the -help output (although, again, they are still visible in the --help-hidden -output).
+output).
-Now the application code can simply use:+
Now the application code can simply use:
... if (!Quiet) printInformationalMessage(...); ... -
- -... which is much nicer! The "cl::alias" can be used to specify an -alternative name for any variable type, and has many uses.
+ +
... which is much nicer! The "cl::alias" +can be used to specify an alternative name for any variable type, and has many +uses.
+| -Selecting an alternative from a set of possibilities - |
So far, we have seen how the CommandLine library handles builtin types like std::string, bool and int, but how does it handle -things it doesn't know about, like enums or 'int*'s?
+things it doesn't know about, like enums or 'int*'s?
-The answer is that it uses a table driven generic parser (unless you specify +The answer is that it uses a table driven generic parser (unless you specify your own parser, as described in the Extension Guide). This parser maps literal strings to whatever type is required, are -requires you to tell it what this mapping should be.
+requires you to tell it what this mapping should be.
-Lets say that we would like to add four optimizations levels to our optimizer, -using the standard flags "-g", "-O0", "-O1", and -"-O2". We could easily implement this with boolean options like above, -but there are several problems with this strategy:+
Lets say that we would like to add four optimizations levels to our +optimizer, using the standard flags "-g", "-O0", +"-O1", and "-O2". We could easily implement this with boolean +options like above, but there are several problems with this strategy:
+ -To cope with these problems, we can use an enum value, and have the CommandLine -library fill it in with the appropriate level directly, which is used like -this:
+
To cope with these problems, we can use an enum value, and have the +CommandLine library fill it in with the appropriate level directly, which is +used like this:
enum OptLevel {
@@ -458,36 +498,36 @@ enum OptLevel {
...
if (OptimizationLevel >= O2) doPartialRedundancyElimination(...);
...
-+ -This declaration defines a variable "OptimizationLevel" of the +
This declaration defines a variable "OptimizationLevel" of the "OptLevel" enum type. This variable can be assigned any of the values that are listed in the declaration (Note that the declaration list must be terminated with the "0" argument!). The CommandLine library enforces that the user can only specify one of the options, and it ensure that only valid enum values can be specified. The "clEnumVal" macros ensure that the command line arguments matched the enum values. With this option added, our -help output now is:
+help output now is:
USAGE: compiler [options] <input file>
OPTIONS:
- Choose optimization level:
+ Choose optimization level:
-g - No optimizations, enable debugging
-O1 - Enable trivial optimizations
-O2 - Enable default optimizations
- -O3 - Enable expensive optimizations
+ -O3 - Enable expensive optimizations
-f - Overwrite output files
-help - display available options (--help-hidden for more)
-o <filename> - Specify output filename
-quiet - Don't print informational messages
-In this case, it is sort of awkward that flag names correspond directly to enum
-names, because we probably don't want a enum definition named "g" in
-our program. Because of this, we can alternatively write this example like
-this:+
In this case, it is sort of awkward that flag names correspond directly to +enum names, because we probably don't want a enum definition named "g" +in our program. Because of this, we can alternatively write this example like +this:
enum OptLevel {
@@ -505,28 +545,30 @@ enum OptLevel {
...
if (OptimizationLevel == Debug) outputDebugInfo(...);
...
-- -By using the "clEnumValN" macro instead of "clEnumVal", we can -directly specify the name that the flag should get. In general a direct mapping -is nice, but sometimes you can't or don't want to preserve the mapping, which is -when you would use it.
+ +
By using the "clEnumValN" macro instead of "clEnumVal", we +can directly specify the name that the flag should get. In general a direct +mapping is nice, but sometimes you can't or don't want to preserve the mapping, +which is when you would use it.
+| -Named Alternatives - |
Another useful argument form is a named alternative style. We shall use this style in our compiler to specify different debug levels that can be used. Instead of each debug level being its own switch, we want to support the following options, of which only one can be specified at a time: "--debug-level=none", "--debug-level=quick", "--debug-level=detailed". To do this, we use the exact same format as our optimization level flags, but we also specify an option name. For this -case, the code looks like this:
+case, the code looks like this:
enum DebugLev {
@@ -534,7 +576,7 @@ enum DebugLev {
};
// Enable Debug Options to be specified on the command line
-cl::opt DebugLevel("debug_level", cl::desc("Set the debugging level:"),
+cl::opt<DebugLev> DebugLevel("debug_level", cl::desc("Set the debugging level:"),
cl::values(
clEnumValN(nodebuginfo, "none", "disable debug information"),
clEnumVal(quick, "enable quick debug information"),
@@ -542,10 +584,10 @@ enum DebugLev {
0));
-This definition defines an enumerated command line variable of type "enum
+This definition defines an enumerated command line variable of type "enum DebugLev", which works exactly the same way as before. The difference here is just the interface exposed to the user of your program and the help output by -the "--help" option:
+the "--help" option:
USAGE: compiler [options] <input file>
@@ -556,60 +598,62 @@ OPTIONS:
-O1 - Enable trivial optimizations
-O2 - Enable default optimizations
-O3 - Enable expensive optimizations
- -debug_level - Set the debugging level:
+ -debug_level - Set the debugging level:
=none - disable debug information
=quick - enable quick debug information
- =detailed - enable detailed debug information
+ =detailed - enable detailed debug information
-f - Overwrite output files
-help - display available options (--help-hidden for more)
-o <filename> - Specify output filename
-quiet - Don't print informational messages
-+ -Again, the only structural difference between the debug level declaration and +
Again, the only structural difference between the debug level declaration and the optimiation level declaration is that the debug level declaration includes an option name ("debug_level"), which automatically changes how the library processes the argument. The CommandLine library supports both forms so -that you can choose the form most appropriate for your application.
- +that you can choose the form most appropriate for your application.
+| -Parsing a list of options - |
Now that we have the standard run of the mill argument types out of the way, lets get a little wild and crazy. Lets say that we want our optimizer to accept a list of optimizations to perform, allowing duplicates. For example, we might want to run: "compiler -dce -constprop -inline -dce -strip". In this case, the order of the arguments and the number of appearances is very important. This is what the "cl::list" template is for. First, start by defining an enum of the optimizations that you -would like to perform:
+would like to perform:
enum Opts {
// 'inline' is a C++ keyword, so name it 'inlining'
dce, constprop, inlining, strip
};
-+ -Then define your "cl::list" variable:
+
Then define your "cl::list" variable:
cl::list<Opts> OptimizationList(cl::desc("Available Optimizations:"), cl::values( clEnumVal(dce , "Dead Code Elimination"), - clEnumVal(constprop , "Constant Propogation"), + clEnumVal(constprop , "Constant Propagation"), clEnumValN(inlining, "inline", "Procedure Integration"), clEnumVal(strip , "Strip Symbols"), 0)); -
+ -This defines a variable that is conceptually of the type +
This defines a variable that is conceptually of the type "std::vector<enum Opts>". Thus, you can access it with standard -vector methods:
+vector methods:
for (unsigned i = 0; i != OptimizationList.size(); ++i) @@ -617,89 +661,143 @@ vector methods:-... to iterate through the list of options specified....
+
... to iterate through the list of options specified.
-Note that the "cl::list" template is completely general and may be used -with any data types or other arguments that you can use with the -"cl::opt" template. One especially useful way to use a list is to -capture all of the positional arguments together if there may be more than one -specified. In the case of a linker, for example, the linker takes several -'.o' files, and needs to capture them into a list. This is naturally -specified as:+
Note that the "cl::list" template is +completely general and may be used with any data types or other arguments that +you can use with the "cl::opt" template. One +especially useful way to use a list is to capture all of the positional +arguments together if there may be more than one specified. In the case of a +linker, for example, the linker takes several '.o' files, and needs to +capture them into a list. This is naturally specified as:
... cl::list<std::string> InputFilenames(cl::Positional, cl::desc("<Input files>"), cl::OneOrMore); ... -
+ -This variable works just like a "vector<string>" object. As +
This variable works just like a "vector<string>" object. As such, accessing the list is simple, just like above. In this example, we used the cl::OneOrMore modifier to inform the CommandLine library that it is an error if the user does not specify any .o files on our command line. Again, this just reduces the amount of -checking we have to do.
+checking we have to do.
+As our program grows and becomes more mature, we may decide to put summary +information about what it does into the help output. The help output is styled +to look similar to a Unix man page, providing concise information about +a program. Unix man pages, however often have a description about what +the program does. To add this to your CommandLine program, simply pass a third +argument to the cl::ParseCommandLineOptions +call in main. This additional argument is then printed as the overview +information for your program, allowing you to include any additional information +that you want. For example:
+ +
+int main(int argc, char **argv) {
+ cl::ParseCommandLineOptions(argc, argv, " CommandLine compiler example\n\n"
+ " This program blah blah blah...\n");
+ ...
+}
+
+
+Would yield the help output:
+ ++OVERVIEW: CommandLine compiler example + + This program blah blah blah... + +USAGE: compiler [options] <input file> + +OPTIONS: + ... + -help - display available options (--help-hidden for more) + -o <filename> - Specify output filename ++ +
| -Reference Guide - |
+
Now that you know the basics of how to use the CommandLine library, this +section will give you the detailed information you need to tune how command line +options work, as well as information on more "advanced" command line option +processing capabilities.
+| -Positional Arguments - |
Positional arguments are those arguments that are not named, and are not specified with a hyphen. Positional arguments should be used when an option is specified by its position alone. For example, the standard Unix grep tool takes a regular expression argument, and an optional filename to search through (which defaults to standard input if a filename is not specified). -Using the CommandLine library, this would be specified as:
+Using the CommandLine library, this would be specified as:
cl::opt<string> Regex (cl::Positional, cl::desc("<regular expression>"), cl::Required); cl::opt<string> Filename(cl::Positional, cl::desc("<input file>"), cl::init("-"));-Given these two option declarations, the --help output for our grep -replacement would look like this:
+
Given these two option declarations, the --help output for our grep +replacement would look like this:
-USAGE: spiffygrep [options] <regular expression> <input file> +USAGE: spiffygrep [options] <regular expression> <input file> OPTIONS: -help - display available options (--help-hidden for more)-... and the resultant program could be used just like the standard grep -tool.
+
... and the resultant program could be used just like the standard +grep tool.
-Positional arguments are sorted by their order of construction. This means that -command line options will be ordered according to how they are listed in a .cpp -file, but will not have an ordering defined if they positional arguments are -defined in multiple .cpp files. The fix for this problem is simply to define -all of your positional arguments in one .cpp file.+
Positional arguments are sorted by their order of construction. This means +that command line options will be ordered according to how they are listed in a +.cpp file, but will not have an ordering defined if they positional arguments +are defined in multiple .cpp files. The fix for this problem is simply to +define all of your positional arguments in one .cpp file.
+Sometimes you may want to specify a value to your positional argument that starts with a hyphen (for example, searching for '-foo' in a file). At first, you will have trouble doing this, because it will try to find an argument named '-foo', and will fail (and single quotes will not save you). -Note that the system grep has the same problem:
+Note that the system grep has the same problem:
$ spiffygrep '-foo' test.txt @@ -710,89 +808,95 @@ Note that the system grep has the same problem:grep: illegal option -- o grep: illegal option -- o Usage: grep -hblcnsviw pattern file . . . -
+ -The solution for this problem is the same for both your tool and the system +
The solution for this problem is the same for both your tool and the system version: use the '--' marker. When the user specifies '--' on the command line, it is telling the program that all options after the '--' should be treated as positional arguments, not options. Thus, we -can use it like this:
+can use it like this:
$ spiffygrep -- -foo test.txt
...output...
-- + +
The cl::ConsumeAfter formatting option is used to construct programs that use "interpreter style" option processing. With this style of option processing, all arguments specified after the last positional argument are treated as special interpreter arguments that are not -interpreted by the command line argument.
+interpreted by the command line argument.
-As a concrete example, lets say we are developing a replacement for the standard -Unix Bourne shell (/bin/sh). To run /bin/sh, first you -specify options to the shell itself (like -x which turns on trace +As a concrete example, lets say we are developing a replacement for the +standard Unix Bourne shell (/bin/sh). To run /bin/sh, first +you specify options to the shell itself (like -x which turns on trace output), then you specify the name of the script to run, then you specify arguments to the script. These arguments to the script are parsed by the bourne shell command line option processor, but are not interpreted as options to the -shell itself. Using the CommandLine library, we would specify this as:
+shell itself. Using the CommandLine library, we would specify this as:
cl::opt<string> Script(cl::Positional, cl::desc("<input script>"), cl::init("-")); cl::list<string> Argv(cl::ConsumeAfter, cl::desc("<program arguments>...")); cl::opt<bool> Trace("x", cl::desc("Enable trace output")); -
+ -which automatically provides the help output:
+
which automatically provides the help output:
-USAGE: spiffysh [options] <input script> <program arguments>... +USAGE: spiffysh [options] <input script> <program arguments>... OPTIONS: -help - display available options (--help-hidden for more) - -x - Enable trace output -
+ -x - Enable trace output + -At runtime, if we run our new shell replacement as 'spiffysh -x test.sh -a --x -y bar', the Trace variable will be set to true, the +
At runtime, if we run our new shell replacement as 'spiffysh -x test.sh +-a -x -y bar', the Trace variable will be set to true, the Script variable will be set to "test.sh", and the -Argv list will contain ["-a", "-x", "-y", "bar"], because -they were specified after the last positional argument (which is the script -name).
+Argv list will contain ["-a", "-x", "-y", "bar"], because they +were specified after the last positional argument (which is the script +name).
-There are several limitations to when cl::ConsumeAfter options can be -specified. For example, only one cl::ConsumeAfter can be specified per -program, there must be at least one positional +There are several limitations to when cl::ConsumeAfter options can +be specified. For example, only one cl::ConsumeAfter can be specified +per program, there must be at least one positional argument specified, and the cl::ConsumeAfter option should be a cl::list option.
- +href="#cl::list">cl::list
option. +| -Internal vs External Storage - |
By default, all command line options automatically hold the value that they parse from the command line. This is very convenient in the common case, especially when combined with the ability to define command line options in the -files that use them. This is called the internal storage model.
+files that use them. This is called the internal storage model.
-Sometimes, however, it is nice to separate the command line option processing +Sometimes, however, it is nice to separate the command line option processing code from the storage of the value parsed. For example, lets say that we have a '-debug' option that we would like to use to enable debug information across the entire body of our program. In this case, the boolean value controlling the debug code should be globally accessable (in a header file, for example) yet the command line option processing code should not be exposed to all of these clients (requiring lots of .cpp files to #include -CommandLine.h).
+CommandLine.h).
-To do this, set up your .h file with your option, like this for example:+
To do this, set up your .h file with your option, like this for example:
// DebugFlag.h - Get access to the '-debug' command line option @@ -811,278 +915,332 @@ extern bool DebugFlag; // // DEBUG(cerr << "Bitset contains: " << Bitset << "\n"); // -#ifdef NDEBUG +#ifdef NDEBUG #define DEBUG(X) #else -#define DEBUG(X) \ +#define DEBUG(X) \ do { if (DebugFlag) { X; } } while (0) -#endif +#endif-This allows clients to blissfully use the DEBUG() macro, or the +
This allows clients to blissfully use the DEBUG() macro, or the DebugFlag explicitly if they want to. Now we just need to be able to set the DebugFlag boolean when the option is set. To do this, we pass an additial argument to our command line argument processor, and we specify -where to fill in with the cl::location attribute:
+where to fill in with the cl::location +attribute: