Using argv in C?

Question

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!

Cavil

Answer 1

The line

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

compares pointers, not strings. Use the strcmp function instead:

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

Infarct

Haha. 6 answers just like mine in the time it took me to write the answer. – Kopaz

Well, that absolutely did it. Thank you for correcting this, I'm very new to C! – Cavil

Answer 2

Change:

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

to

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

and include string.h.

Elocution

Answer 3

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

Anthesis

Answer 4

You can't compare c-strings like that. Use strcmp (reference here).

Because c-strings are actually pointers, the == operator compares the address of the first character which will never be equal in this case.

Lixiviate

Answer 5

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:

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

Irs

Answer 6

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

Bendicta