Command-line arguments in C

argv[0] is the program name, and argv[argc] is always NULL.

#include <stdio.h>

int main(int argc, char **argv) {
    if (argc < 2) {
        fprintf(stderr, "usage: %s WORD...\n", argv[0]);
        return 1;
    }

    for (int i = 1; i < argc; i++) {
        printf("%d: %s\n", i, argv[i]);
    }

    printf("argv[argc] is NULL: %d\n", argv[argc] == NULL);
    return 0;
}

How it works

1. argc counts the program name too, so options start at one.
2. Every argument arrives as a NUL-terminated string.
3. Returning non-zero from main signals failure to the shell.

Keywords and builtins used here

• NULL
• char
• for
• if
• int
• main
• return

The run, in numbers

Lines

15

Characters to type

267

Tokens

93

Three-star pace

95 tpm

At the three-star pace of 95 tokens a minute, this run takes about 59 seconds.

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Step 1 of 4 in Program environment, step 1 of 14 in Systems programming.

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