An easy-to-use command-line argument parsing library for C
Sealarg is a command-line parsing library designed to be as straightforward as possible to use. It is a small wrapper around the POSIX getopt/GNU getopt_long utilities, written to hide the grunt work and learning curve associated with the getopt interface. Skip to the Getting Started section below for a demonstration of Sealarg in action and how to quickly begin integrating the library into your project.
While getopt itself is a solid, standardized approach to command-line parsing, learning enough about it to attain a desirable level of robustness can often get in the way of the actual project it's being used in. Getopt has been widely used for decades and inspired many similar libraries in other languages, however other libraries such as Python's argparse have been developed with the intent of providing a much simpler alternative to verbose argument parsing. As such, this library lends much of its design choices to these newer alternative libraries.
The sample code below illustrates just how easy Sealarg is to use in 5 steps. Here our program takes a string as a positional argument and prints it. If the optioanl argument -m/--multiple is used, the program prints out the string as many times as specified by the value passed to the option.
#include "sealarg.h"
int main(int argc, char **argv) {
int i;
int count;
char *str;
// 1. Allocate a SealParser instance
SealParser *parser = malloc(sizeof(SealParser));
// 2. Initialize the parser
Initialize(parser, "Prints a string some number of times", "This is a prologue", "This is an epilogue", PS_SEAL);
// 3. Add any number of optional or positional arguments
AddArgument(parser, "m", "multiple", "Number of string instances to print", AK_OPTIONAL, AR_REQUIRED, AA_VALUE, VT_INT);
AddArgument(parser, NULL, "string", "String to be printed", AK_POSITIONAL, AR_REQUIRED, AA_VALUE, VT_STRING);
// 4. Parse all the arguments and check for any errors
Parse(parser, argc, argv);
if(parser->err != 0) {
free(parser);
return parser->err;
}
// 5. Access arguments by index in the order they were added to the parser
count = parser->args[1].value.i;
str = parser->args[2].value.cp;
for(i = 0; i < count; i++) {
printf("%s\n", str);
}
free(parser);
return 0;
}When compiled and run with the -h/--help option, the following usage statement is automatically built and printed:
$ ./sample_program -h
Usage: sample_program [-h] [-m MULTIPLE] STRING
Prints a string some number of times
This is a prologue
Positional Arguments:
STRING String to be printed
Optional Arguments:
-h, --help Display this help message and exit
-m, --multiple Number of string instances to print
This is an epilogue
$
Things like missing/excessive arguments, invalid arguments, and basic type/limit checking are all handled automatically.
To integrate Sealarg into your project:
- Copy
src/sealarg.candinclude/sealarg.hinto your project folder and add them as dependenices in your Makefile, just like the rest of your code files - Add
#include "sealarg.h"to wherever you'll be dealing with command-line arguments- typically this would be the .c file containing yourmainfunction - Try compiling to make sure the library can be built alongside your code without any issues. If so, you're ready to start making calls to Sealarg's API and parse some arguments!
For additional examples, check out example/
For full documentation of Sealarg's API, including its more advanced semantics and finer-grained control, check out doc/
Want to learn more about getopt? Click the links below: