Question

I'm trying to use the execvp() command with an array of strings initialized like: char arr[4][100];

in this array I have the program executable (arr[0]), and its arguments (arr[1], arr[2], arr[3]) stored.

The man page for execvp requires:

execvp(filepath, char *args[])

I was wondering if I could convert the contents of my char arr[][] array into an array of char *arr[]???

Answer 1

C CODES:

/* hello.c */
/* This is the program to be executed using execvp() */

#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[]){
        printf("Called by main.c using execvp()\n");
        printf("Argument list argv:\n");
        for(int i = 0; i < argc; i++)
                printf("argv[%d] = %s\n", i, argv[i]);
        return 0;
}

/* END OF hello.c */


/* main.c */
/* This is the function which calls hello.c using system call execvp() */

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

int main() {
        // This is your 2 dimensional char array
        char arr[4][100] = {"./hello", "arg1", "arg2", "arg3"};

        char *cmd = arr[0];// This is the command used to run the program
        char *argv[5];// This is the arguments list

        argv[0] = "/home/shubham/temp/hello";//  This the filename with full path
        argv[1] = arr[1];// First argument to the program
        argv[2] = arr[2];// Second argument to the program
        argv[3] = arr[3];// Third argument to the program
        argv[4] = NULL;// This is NULL and is very important to tell that argument list is over

        execvp(cmd, argv);// Call hello.c
        return 0;
}

/* END OF main.c */

OUTPUT:

• Compile hello.c and create an executable named hello:
  
  
• Compile main.c and create an executable named main:
  
  
• Execute main using ./main
  

NOTE: Don't forget to add NULL at the end of the arguments list.

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