Pass File Descriptor - Execve (typecast)

Question

I am wondering how I can pass a file descriptor through the execve() command and then access it on the other side. I know that I can use dup2 to re

Answer 1

Simply casting the file descriptor to a char* isn't a good idea. It could cause data loss if the OS chooses to copy the strings and stops at the 0 bytes, so the data isn't entirely copied. It would be safer to create a string containing the file descriptor.

int pfd[2];
if(pipe(pfd) == -1)
    exitWithError("PIPE FAILED", 1);
char string1[12]; // A 32 bit number can't take more than 11 characters, + a terminating 0
snprintf(string1,12,"%i",pfd[1]); // Copy the file descriptor into a string
char *args_1[] = {"reader", argv[1], &string1[0], (char *) 0};

The reader program then uses atoi to convert this back into an int.

int fd = atoi(argv[2]);
write(fd,buf,read_test);

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If you really want to use a cast, then you need to cast argv[2] as int* in your reader.

write(((int*)argv[2])[1],buf,read_test);