CODEWITHSUNDEEP
c++charint
rzeto
rzeto

Reputation: 1

C++ char* to int error

I would like to take a command line argument (which will be an integer greater than zero) and use it as an integer parameter in a function (to decide which part of the function to use).

double func(double x, double y, double z, int n) {
  if (n==1) { return 1; } 
  if (n==2) { return 2; }
  // etc
}
int main (int argc, char *argv[]) {
  int n = argv[1];
  // etc, later I call func(x,y,z,n) with this definition of n
}

When I try to compile, I get some warnings: 

warning: invalid conversion from ‘char*’ to ‘int’
warning: initializing argument 4 of ‘double func(double, double, double, int)’

I think I understand why it's happening, I just don't know how to fix it. Nothing I've found so far googling has been too helpful. I'm quite new at C++, and any information that'd point me in the right direction would be great. Thank you for your time.

Upvotes: 0

Views: 2027

Answers (2)

Dietmar Kühl
Dietmar Kühl

Reputation: 153792

You can use std::istringstream to convert the number:

int main(int ac, char * av[]) {
    int av1;
    if (2 <= ac
        && std::istringstream(av[1]) >> av1) {
        do_something_with(av1);
    }
    else {
        report_error();
    }
}

Upvotes: 1

P.P
P.P

Reputation: 121347

argv[1] is of type char*. Convert it to integer using strtol:

char *ptr;
int n = strtol(argv[1], ptr, 10);
/* Error checking */

Upvotes: 1

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