echo variable in c program

Question

I have a program written in C language(admin-secret) that has a function called authenticate. Inside this function there is a variable called "result". How do i echo this variable using another c program?
The purpose of this is to guess the password using strncmp return value.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{     
    char command[1000] = {0};
    int result;
    sprintf(command, "/home/alice/Public/admin-secret %s; echo  %d", argv[1], result);
    system(command);
    printf("Result: %s\n" , result);
    return 0;
}

Answer 1

You need to create a pipe, an easy way to do it is by using the POSIX function popen().

#include <stdio.h>

int main(int argc, char* argv[])
{
    FILE *pipe;
    char line[256];
    pipe = popen("ls", "r");
    if (pipe != NULL)
    {
        while (fgets(line, sizeof(line), pipe) != NULL)
            fprintf(stdout, "%s", line);
        pclose(pipe);
    }
    return 0;
}

You can build the command with sprintf()¹ too and pass it as the first parameter to popen(), this is just to show you how you can capture the output of another program.

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¹_{You should really use snprintf() to prevent overflowing the destination array}