Reputation: 125

Using argv in C?

For an assignment, I am required to have command line arguments for my C program. I've used argc/argv before (in C++) without trouble, but I'm unsure if C style strings are affecting how this works. Here is the start of my main:

int main(int argc, char *argv[]){

  if(argc>1){
    printf("0 is %s, 1 is %s\n",argv[0],argv[1]);
    if(argv[1]=="-e"){
        // Do some stuff with argv[2]
        system("PAUSE");
    }
    else{
        printf("Error: Incorrect usage - first argument must be -e");
        return 0;
    }
  }

So I am calling my program as "program.exe -e myargstuff" but I am getting the "Error: Incorrect Usage..." output, even though my printf() tells me that argv[1] is "-e". Some help, please? Thanks!

Upvotes: 10

Answers (6)

zneak

Reputation: 138051

The prototype of the main function says you're dealing with char* pointers. In C, there is no operator overloading; therefore, == between two char* will test if they point to the same place. This is not the case, and is rarely the case at all. Use the strcmp (the reference for the function is valid even though it points to a C++ site) function from <string.h>:

strcmp(argv[1], "-e") == 0

Upvotes: 1

Carl Norum

Reputation: 224904

Check out getopt() and related functions; it'll make your life a lot easier.

Upvotes: 5

Dawid

Reputation: 4062

Change:

if(argv[1]=="-e"){

if(strcmp(argv[1], "-e") == 0){

and include string.h.

Upvotes: 7

Laurence Gonsalves

Reputation: 143154

You can't use == to compare strings like that in C. That's just comparing the addresses of argv[1] and your literal, which are pretty much guaranteed to be different.

Use strcmp instead. eg: