A simplified command line parser which intialize itself by parsing the usage text.
Unlike other comand line parsers, where the command options have to be added to the parser before parsing, the construction of this command line parser is done by parsing the usage text, which is supposed to be provided anyway.
Using the usage text as the input of the parser help the author to keep the usage text and the actual usage consistent as they are from the same source.
The following shows an example to demonstrate how simple it is to use the CmdOption to construct the parser and pasre the command line.
This example is a simple divider program. The task of the program is simply divide two integers. For demostration purpose, a few options are added.
// FILE: divider.cpp
#include "CmdOption.h"
int main(int argc, char **argv) {
tianbo::CmdOption command_opt;
// Add the usage text. This usage message is not only used as a help message, but also as the input for the
// CmdOption object to initialize itself.
command_opt << R"(
Divider two integers.
Usage: divide [options] a b
Options:
-w --warning
Warn if the divisor is zero
This option has no parameter, i.e. it is a switch
-p --precision=NUM
Controls the precision of the output
This option does not have a short option for it and an argument could be assigned to it.
Note that "NUM" is informative only to the reader of the message, not to the parser.
-f FILE
Save the result into a file.
There is no long option for the option. This option also needs an argument. In this form,
explanation must be in a separate line
-h --help Show this help message.
Description text can be at the same line of the options
Examples:
The following command divide 5 by 3
divide 5 3
The command will print 1.66666666666667. To get a short answer, a precision option can be added.
For example:
divide --precision=3 5 3
Get a warning if the divisor is zero
divide -w 5 0
... Add more description as needed.
)";If the usage message does not follow the protocol, the parser may not be able to parse it properly thus not able to parse the command line. You can use the function reportError() to show the detail of the problem if there is any error in the text.
command_opt.reportError();This line should be removed once debugging is done.
The command line is parsed by calling the function parse()
command_opt.parse(argc, argv);The [] operator is used to access the switch. The following shows how to
check if -h option is given. Alternatively, this switch can be checked with
command_opt["help"]
if (command_opt["h"]) {
command_opt.usage();
return 0;
}Internally, the [] operator returns a StringValue type, which can be
interpreted as a boolean to tell if it has been set.
bool show_warning = (bool)command_opt["w"];The "precision" option has no short form. It has to be accessed with the long
option. The StringValue returned by [] operator can be converted to an integer.
int precision = command_opt["precision"].valueOr(15);It is equivalent to
int precision = 15;
if (command_opt["precision"])
precision = command_opt["precision"];The command line arguments are accessible through function arguments()
if (command_opt.arguments().count() != 2) {
std::cerr << "No operands provided" << std::endl;
return 1;
}The arguments can be converted into a vector of integers or other data types
std::vector<int> operands = command_opt.arguments();
if (show_warning && operands.back() == 0) {
std::cerr << "The divisor is zero!" << std::endl;
return 2;
}
The rest is do the simple calculation, which can be found in the file example.cpp