Calling executable file inside C program

Question

I have a C program which will take one argument as input and, if the argument is matching with the string inside the executable, it will return 1 otherwise 0. The executable file name is prg1. I have some input strings in a file named inputs.txt. I want to get those strings from the input file and call the prg1 inside a C program with each string.

I have tried the following code but it's not working.There is no segmentation fault but when i am calling prg1 it executes, Because the printf() statement inside prg1 is working and i can see the output.it changes variable found to 0I cant change the prg1. Because my friend has given the executable file of that program to me, not the source code. Header files are stdio.h and string.h

int main()
{
    FILE *fk;
    char text[80],inp[16],test[50]={"./prg1 "};
    int found=100;
    fk=fopen("inputs.txt","r");
    while((fscanf(fk,"%s",inp))!=EOF)
    {
        strcat(test,inp);
        found=system(test);
        if(found==1)
        {
            printf("\nAnswer is   : %s",inp);
            break;
        }
            strcpy(test,"./prg1 ");

    }
    fclose(fk);
    return 0;
}

What is wrong with my code?

Please, next time include the libraries you have included, and a specific error message. For others: Once compiled and run it quits with a Segmentation Fault. edit Whoops, that is if you do not have an inputs.txt. Make sure you do when testing! — Yuri

Ptival Ptival · Accepted Answer · 2011-03-19T14:43:06

I am not sure of what you want to achieve but here are some comments:

1 - You should test the return value of fopen:

if (!fk) { ... }

2 - You're not cleaning the test buffer between each test, so you are effectively calling:

system("prg1 first_word");
system("prg1 first_wordsecond_word");
...

You should have something like:

strcpy(test, "prg1 ");

after entering the loop and before strcat.

3 - Do you have spaces in your input strings? You should fix your code to read until a newline in this case.

4 - You might want to use EXIT_SUCCESS and EXIT_FAILURE instead of 0 and 1.

Calling executable file inside C program

3 Answers