Running a program

This is a discussion on Running a program within the C Programming forums, part of the General Programming Boards category; Hello, I'm just starting to program in Unix and I want to execute a binary. The program that I execute ...

  1. #1
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    Running a program

    Hello,
    I'm just starting to program in Unix and I want to execute a binary. The program that I execute gets user input from standard input and prints it out. How would I run the program then print to the standard in?

    I know that execl("./program"... ); works to run the program but I'm not sure how to give it input.

  2. #2
    Registered User Mortissus's Avatar
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    Just type "./program_name" at your console. No need to use execl. To read input, use fscanf function, for example
    Code:
    #include <stdio.h>
    
    int main(){
    
       int n;
    
       printf("Enter a number\n");
    
       //read from standard input
       fscanf(stdin, "%d", &n);
    
       printf("Number entered is %d\n", n);
    
    
       return 0;
    
    }

  3. #3
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    Yes, but I need to be able to execute the program from within another program.

  4. #4
    Frequently Quite Prolix dwks's Avatar
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    You would pass the program arguments. From the command line:
    Code:
    $ program arg1 arg2 argn
    In the program:
    Code:
    int main(int argc. char *argv[]) {
        int x;
    
        if(argc > 1) for(x = 1; x < argc; x ++) {
            printf("\nArgument %i: %s", x, argv[x]);
        }
        else printf("\nNo arguments passed\n");
    
        printf("\n");
    
        return 0;
    }
    I don't know how you run a program from another program in Linux. On my DOS machine it's system(), in stdlib.h. system() will probably work on your machine. But you can use execl() too if you want to.
    dwk

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  5. #5
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    system() is a standard function - it should work for any correct C/C++ implementation. It will just execute the string given to it in the system shell - and that's where the dangers starts. If you know that your program will only be run on your OS, than most of the problems become moot points.

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    The problem is when you run System() it runs until the program ends, and if the program must have input then it will never end... Correct?

  7. #7
    ATH0 quzah's Avatar
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    Perhaps popen is what you're looking for.

    Quzah.
    Hope is the first step on the road to disappointment.

  8. #8
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    Quote Originally Posted by quzah
    Perhaps popen is what you're looking for.

    Quzah.
    I tried popen, but it didnt give me what I wanted, it printed what I wanted to the screen, but it didn't input it to the program.

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