CODEWITHSUNDEEP
carraysexecv
earlymorningtea
earlymorningtea

Reputation: 508

sprintf() command doesnt work

I am trying to write an c program which get two float numbers from user and then calls another program with execv() command. But I can't do it , because of converting float to char or I don't know why. The problem is execv() command is not working; the output must be like that

Enter first num: 5
Enter second num: 7
5.000000 + 7.000000 = 12.000000
parentPID: 9745 childPID: 9746 works now

but it is is like that now

Enter first num: 5
Enter second num: 7
parentPID: 9753 childPID: 9754 works now

my first c program sum.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int main(int argc, char **argv) {
  if(argc!=3)
  printf("error...\n");
  double a=atof(argv[1]);
  double b=atof(argv[2]);
  printf("%lf + %lf = %lf \n",a,b,a+b);
  return 0;
}

and the second program calculate.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
int main() 
{
  float x,y;
  pid_t pid;

  printf("Enter first num: ");
  scanf("%f",&x);
  printf("Enter second num: ");
  scanf("%f",&y);

  if((pid=fork())== -1)
  {
    printf("can not fork..\n");
    exit(1);
  }
  if(pid==0) //child
  {

    pid=getpid();
    char *temp[] = {NULL,NULL,NULL,NULL};
    temp[0]="sum";
    sprintf(*temp[1],"%f",x); //here I want to convert float number to char but it doesn't work
    sprintf(*temp[2],"%f",y);
    execv("sum",temp);
  }
  else
  {
    wait(NULL);
    printf("parentPID: %d childPID: %d works now.\n", getpid(), pid);
  }

  return 0;
}

Upvotes: 0

Views: 9301

Answers (1)

Mohit Jain
Mohit Jain

Reputation: 30489

char command1[50], command2[50]; // Added
char *temp[] = {NULL, command1, command2, NULL}; // Modified
temp[0]="sum";
sprintf(temp[1],"%f",x); // remove *
sprintf(temp[2],"%f",y); // remove *

You are not allocating to temp[1] and temp[2] and using those as destination buffer in sprintf and using incorrect * in sprint.

You can use malloc to allocate this memory or use other string as shown in above example to initialize the array.

From kind comment of Sourav Ghosh:

In sum.c, change below lines of code to:

if(argc!=3)
{
  printf("error...\n");
  return -1;
}

or else, it may lead to undefined behaviour.

Upvotes: 5

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