How to read an argument in from command line into a double?

Question

This program is first forked then run by execlp, it's calling program passes in two numbers, a power and a base.

int main(int argc, char *argv[])
{
    int pid = getpid();
    printf("Calculator Process[%d]: started\n",pid);
    double base, power;
    sscanf(argv[1],"%d",&base);
    sscanf(argv[2],"%d",&power);
    double number = pow(base,power);
    printf("Calculator Process[%d]: %d ^^ %d == %d\n",pid,base,power,number);
    printf("Calculator Process[%d]: exiting\n",pid);
    return 1;
}

Lets say I pass into it base 3, power 5. This is what I get:

base = 4263 -- this also happens to be the PID. 
power = -1 
raised to power: 714477568

Calling line:

execlp("./calculator","./calculator",argv[1],argv[2],(char*)0);

When I print the argvs, I get their value (as a char*, but casting fails).

Any ideas why I can't get the values to be correctly read in?

Answer 1

Either read double:

double base, power;
sscanf(argv[1],"%lf",&base);
sscanf(argv[2],"%lf",&power);

Or scan into integers:

int base, power;
sscanf(argv[1],"%d",&base);
sscanf(argv[2],"%d",&power);

Answer 2

A quick adjustment of your code should do it:

int main(int argc, char *argv[]) 
{
    int pid = getpid();
    printf("Calculator Process[%d]: started\n",pid);
    double base, power;
    base = atof(argv[1]);
    power = atof(argv[2]);
    double number = pow(base,power);
    printf("Calculator Process[%d]: %f ^^ %f == %f\n",pid,base,power,number);
    printf("Calculator Process[%d]: exiting\n",pid);
    return 1; 

}

1. For converting a char array to a digit you can use atof()
2. Don't forget to update the printf to a double %f or they won't display right in your output!