To my knowledge, the three most popular ways how to parse command line arguments in C are:
- Getopt (
#include <unistd.h> from the POSIX C Library), which can solve simple argument parsing tasks. If you're a bit familiar with bash, the getopt built-in of bash is based on Getopt from the GNU libc.
- Argp (
#include <argp.h> from the GNU C Library), which can solve more complex tasks and takes care of stuff like, for example:
-?, --help for help message, including email address-V, --version for version information--usage for usage message
- Doing it yourself, which I don't recommend for programs that would be given to somebody else, as there is too much that could go wrong or lower quality. The popular mistake of forgetting about '--' to stop option parsing is just one example.
The GNU C Library documentation has some nice examples for Getopt and Argp.
Example for using Getopt
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
bool isCaseInsensitive = false;
int opt;
enum { CHARACTER_MODE, WORD_MODE, LINE_MODE } mode = CHARACTER_MODE;
while ((opt = getopt(argc, argv, "ilw")) != -1) {
switch (opt) {
case 'i': isCaseInsensitive = true; break;
case 'l': mode = LINE_MODE; break;
case 'w': mode = WORD_MODE; break;
default:
fprintf(stderr, "Usage: %s [-ilw] [file...]
", argv[0]);
exit(EXIT_FAILURE);
}
}
// Now optind (declared extern int by <unistd.h>) is the index of the first non-option argument.
// If it is >= argc, there were no non-option arguments.
// ...
}
Example for using Argp
#include <argp.h>
#include <stdbool.h>
const char *argp_program_version = "programname programversion";
const char *argp_program_bug_address = "<[email protected]>";
static char doc[] = "Your program description.";
static char args_doc[] = "[FILENAME]...";
static struct argp_option options[] = {
{ "line", 'l', 0, 0, "Compare lines instead of characters."},
{ "word", 'w', 0, 0, "Compare words instead of characters."},
{ "nocase", 'i', 0, 0, "Compare case insensitive instead of case sensitive."},
{ 0 }
};
struct arguments {
enum { CHARACTER_MODE, WORD_MODE, LINE_MODE } mode;
bool isCaseInsensitive;
};
static error_t parse_opt(int key, char *arg, struct argp_state *state) {
struct arguments *arguments = state->input;
switch (key) {
case 'l': arguments->mode = LINE_MODE; break;
case 'w': arguments->mode = WORD_MODE; break;
case 'i': arguments->isCaseInsensitive = true; break;
case ARGP_KEY_ARG: return 0;
default: return ARGP_ERR_UNKNOWN;
}
return 0;
}
static struct argp argp = { options, parse_opt, args_doc, doc, 0, 0, 0 };
int main(int argc, char *argv[])
{
struct arguments arguments;
arguments.mode = CHARACTER_MODE;
arguments.isCaseInsensitive = false;
argp_parse(&argp, argc, argv, 0, 0, &arguments);
// ...
}
Example for Doing it Yourself
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
bool isCaseInsensitive = false;
enum { CHARACTER_MODE, WORD_MODE, LINE_MODE } mode = CHARACTER_MODE;
size_t optind;
for (optind = 1; optind < argc && argv[optind][0] == '-'; optind++) {
switch (argv[optind][1]) {
case 'i': isCaseInsensitive = true; break;
case 'l': mode = LINE_MODE; break;
case 'w': mode = WORD_MODE; break;
default:
fprintf(stderr, "Usage: %s [-ilw] [file...]
", argv[0]);
exit(EXIT_FAILURE);
}
}
argv += optind;
// *argv points to the remaining non-option arguments.
// If *argv is NULL, there were no non-option arguments.
// ...
}
Disclaimer: I am new to Argp, the example might contain errors.
