how to use execvp() and fclose()? - c

Question

I'm making a program that reads a text file with different numbers each line and put that numbers in a string. (could be in a array of integer but I need to use the function execvp so I guess i need do as a string). Then it uses a second program to calculate the square of that numbers.
The problem is: I can't pass the arguments to the functions execvp and function execvp is not working. (I guess is something with the fopen)
Edit: I tried with popen instead of execvp and didn't work as well
Here it goes part of my code:
#define LSIZ 128
#define RSIZ 10
char line[RSIZ][LSIZ];
FILE *fptr = NULL;
int i = 0;
int tot = 0;
fptr = fopen("casosproduto.txt", "r");
while(fgets(line[i], LSIZ, fptr))
{
line[i][strlen(line[i]) - 1] = '\0';
i++;
}
fclose(fptr);
char* argument_list3[]={"produto",&line[i],NULL};
tot = i;
for(i = 0; i < tot; ++i)
{
execvp("./produto",argument_list3);
printf(" %s\n", line[i]);
}

Answer 1

execvp will load produto to the original process space, and then execute it, which is equivalent to executing the for loop only once, you can first fork a subprocess and call execvp in the subprocess, Like this
for (i = 0; i < tot; ++i) {
char *argument_list3[] = {"produto", line[i], NULL};
if (fork() == 0) {
execvp("./produto", argument_list3);
}
}
You can also call function system to execute, and you can read a line and execute it once, so it is not limited by the number of lines in the file, e.g:
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#define LSIZ 128
int main()
{
char line[LSIZ];
char cmd[LSIZ + 16];
FILE *fptr = NULL;
fptr = fopen("casosproduto.txt", "r");
if (fptr == NULL)
return -1;
while (fgets(line, LSIZ, fptr)) {
line[strlen(line) - 1] = '\0';
snprintf(cmd, sizeof(cmd), "./produto %s", line);
system(cmd);
}
fclose(fptr);
return 0;
}

Answer 2

Udpdate. I did some changes in my code but still dont work.
Here it goes the code updated:
#define LSIZ 128
#define RSIZ 10
char line[RSIZ][LSIZ];
FILE *fptr = NULL;
int i = 0;
int tot = 0;
fptr = fopen("casosproduto.txt", "rt");
while(fgets(line[i], LSIZ, fptr))
{
line[i][strlen(line[i]) - 1] = '\0';
i++;
}
fclose(fptr);
tot = i;
pid = fork();
for(i = 0; i < tot; i++)
{
char* argument_list3[]={"produto",line[i],NULL};
if (fork() == 0) {
execvp("./produto", argument_list3);
}
}
}
return 0;
}
There are two reasons for the execvp not working...
first- Something related with the fclose function. If i put the fclose function inside the loop (I know that doesn't make sense but just for tests) then it executes the execvp. Outside the loop it doesnt.
Second- Are my arguments to the execvp alright? (when I tested puting the fclose inside the loop i had to change to this "char* argument_list3[]={"produto","4",NULL};" to test with a number, otherwise the result would be always 1.