CODEWITHSUNDEEP
shellcexec
user680136
user680136

Reputation: 9

Program that uses exec() on itself - value problem

I am trying to write a program where it execs itself N times, and each time it execs itself a value x starting from 1 is incremented. N should be the only argument of the program.

For example:

./exec_test.o 4

will print:

Exec: 1
Exec: 2
Exec: 3
Exec: 4
Execs done

I only succeeded in making my values decrease from 4 instead of increase to 4:

Here is my code

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

int main(int argc, char** args){

        if (argc<2){    //Argument error handling
                fprintf(stderr,"Usage %s number_of_iter",args[0]);
                exit(EXIT_FAILURE);
        }
        int x = atoi(args[1]);  //x = the argument used when executing
        *args[1]-=1;    //decrement the argument value
        if (x>0){
                printf("Exec : %d \n",x);       //printing current argument
                execv(args[0],args);            //exec itself with argument decremented
                perror(args[0]);
                exit(1);
        }
                printf("Execs done \n");

}

and executing it results in this:

Exec: 4
Exec: 3
Exec: 2
Exec: 1
Execs done

Is it possible to make x increment from 1 instead of decrease from N while using only one argument for the program?

Upvotes: 0

Views: 135

Answers (1)

MikeCAT
MikeCAT

Reputation: 75062

Yes. You can hold two information (current and maximum count) in one argument.

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

int main(int argc, char** args){

        if (argc<2){    //Argument error handling
                fprintf(stderr,"Usage %s number_of_iter",args[0]);
                exit(EXIT_FAILURE);
        }
        int max, x = 1; // set x to 1 for the first iteration (it will fail to read x)
        char next_argument[128];
        char* next_args[3];
        sscanf(args[1], "%d_%d", &max, &x);
        if (x <= max){
                printf("Exec : %d \n",x);       //printing current argument
                // create next argument
                snprintf(next_argument, sizeof(next_argument), "%d_%d", max, x + 1);
                next_args[0] = args[0];
                next_args[1] = next_argument;
                next_args[2] = NULL;
                execv(args[0],next_args);            //exec itself with argument incremented
                perror(args[0]);
                exit(1);
        }
        printf("Execs done \n");

}

Upvotes: 1

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