Question

I am reading codes of mcachefs and could not understand some codes, like below:

printf("mcachefs " __MCACHEFS_VERSION__ " starting up...\n");

if (argc == 1 || argv[1][0] == '-')
{
    fprintf(stderr,
        "\tError : first argument shall be the the mcachefs_mountpoint !\n");
    exit(2);
}

I have two questions:
1: For printf("mcachefs " __MCACHEFS_VERSION__ " starting up...\n"), is it the correct way to use printf? I have never seen such way of using it.

1. What is the meaning of argv[1][0]? I know argv[] represents the arguments from the command line. But, is not it a one dimension array?

Answer 1

1. When the C compiler sees a lot of string literals next to each other, it concatenates them into one long string. So that use of printf() is OK, as long as the macro __MCACHEFS_VERSION__ expands to a string. That string had better not contain any percent characters… I’d write it as

   printf("mcachefs %s starting up...\n", __MCACHEFS_VERSION__);

2. As others have pointed out, argv[1] is the second string in the string array argv, and strings are character arrays so argv[1][0] is the first character in the second string.