How to pass "*" argument to main()?

Question

I wrote a program that can accepts arguments from the command line, which are supposed to be a number, an operator (of length 1) and another number:

int main(int argc , char *argv[]){
    if (argc < 4){
        printf("Too few arguments (4 required)");
        return -1;
    }

    char *a = argv[1];
    char b = *argv[2];
    char *c = argv[3];

    printf("%s %c %s = ...", a, b, c);
    return 0;
}

Which seems to work fine, such as when I pass 110 + 11 I get:

110 + 11 = ...

But if I pass something with the operator *, like 110 * 11, it messes up:

110 b c_nums.cbp = ...

The only thing that seems to work is if I replace * with ^* or '*' and change char b = *argv[2]; to char b = *(argv[2]+1);

I'm assuming this has to do with how cmd or whatever formats commands, but how can I fix this without always passing ^<op> instead of <op>?

Edit: Ok, so it looks like "*" works in cmd but not Code::Blocks for some reason.

this is because the shell will expand the * to a list of files. You need to quote the * when you run the program — pm100, Oct 12 '18 at 15:30
If four arguments are required, change expression to: `(argc != 4)`. — Fiddling Bits, Oct 12 '18 at 15:30
see https://stackoverflow.com/questions/11456403/stop-shell-wildcard-character-expansion — pm100, Oct 12 '18 at 15:31
This has nothing to do with C, it is the shell which you are calling your program from. You could also use `\*` — cdarke, Oct 12 '18 at 15:31
The quotes are stripped by the shell before the program is called. — cdarke, Oct 12 '18 at 15:32
you actually solved it yourself by using '*' - ie quoting the * — pm100, Oct 12 '18 at 15:35
i would suggest passing the calcuation as a single string - ie `myprog '12 * 34 - 42' — pm100, Oct 12 '18 at 15:36
@AnttiHaapala The Windows command prompt doesn't have special treatment for `*`. Globbing is done by individual commands. — dbush, Oct 12 '18 at 15:40
Yes but is this something like some MinGW startup routine or sometihng? — Antti Haapala -- Слава Україні, Oct 12 '18 at 15:42

score 1 · Answer 1 · answered Oct 12 '18 at 15:31

1

The * character has special meaning to the shell. It gets interpreted before your program is even executed.

You need to escape the * from the shell in order for your program to see it, either by preceeding it with a backslash or enclosing it in quotes.

answered Oct 12 '18 at 15:31

dbush

205,898
23
218
273

Good catch. A wildcard. – nicomp Oct 12 '18 at 15:38

How to pass "*" argument to main()?

1 Answers1