how to use correctly fork() and exec()

问题:

I have this code;

pid_t process;
process = fork();

if (process < 0){
   //fork error
   perror("fork");
   exit(EXIT_FAILURE);
}
if (process == 0){
   //i try here the execl
   execl ("process.c", "process" , n, NULL);
}
else {
   wait(NULL);
}

I don't know if this use of fork() and exec() combined is correct. When I try to run the program from the bash I do not receive any result, so I thought it could be a problem in this part of code.
Thanks.

回答1:

One problem is that

if (process = 0){

should read

if (process == 0){

Otherwise you're assigning zero to process and only calling execl if result is non-zero (i.e. never).

Also, you're trying to exec something called process.c. There's no doubt that one could have an executable called process.c. However, conventionally names ending in .c are given to C source code files. If process.c is indeed a C file, you need to compile and link it first.

Once you've built the executable, you need to either place it somewhere on $PATH or specify its full path to execle(). In many Unix environments placing it in the current directory won't be enough.

Finally, it's unclear what n is in the execle() call, but the name hints at a numeric variable. You need to make sure that it's a string and not, for example, an integer.

回答2:

Well as per the answers and comments above your code should look somewhat like this

pid_t process;
process = vfork(); //if your sole aim lies in creating a child that will ultimately call exec family functions then its advisable to use vfork

if (process < 0)
{
  //fork error
  perror("fork");
  exit(EXIT_FAILURE);
}
if (process == 0)
{
  //i try here the execl
  char N[MAX_DIGITS];//A correction here
  itoa(n,N);//write this function yourself
  execl ("process", "process" , N, NULL);// Here process is the name of the executable N is your original argument
  fprintf(stderr,"execl failed\n");//check for error in execl

}
else
{
  wait(NULL);
}

Notice the use of vfork instead of fork.Its because it would be much more efficient.The reason could be found here