How to compile in Xcode C file with C11 language dialect? - xcode

Question

I want to compile this source code:
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
int main(int argc, const char *argv[]) {
While:
printf("MacBook-Pro-...:~ ...$ ");
char command[128];
gets_s(command);
if (strncmp(command, "exit", 4) == 0)
exit(0);
pid_t return_value = fork();
if (return_value == 0) {
int outfile;
if ((outfile = dup(1)) == -1)
return -1;
close(1);
if ((outfile = open("/Users/.../1.txt",
O_WRONLY | O_TRUNC | O_CREAT, 0644)) >= 0) {
execl("/bin/sh", "sh", "-c", command, NULL);
}
close(outfile);
exit(0);
} else {
wait();
FILE *fp;
char str[128];
fp = fopen("/Users/.../1.txt", "r");
while(!feof(fp)) {
if(fgets(str, 126, fp))
printf("%s", str);
}
fclose(fp);
goto While;
}
return 0;
}
But i have some errors:
Semantic Issue
Implicit declaration of function 'gets_s' is invalid in C99
Implicitly declaring library function 'exit' with type 'void (int) attribute((noreturn))'
Implicit declaration of function 'wait' is invalid in C99
Too few arguments to function call, expected 1, have 0
Project settings:
System:
ProductName: Mac OS X
ProductVersion: 10.12.1
BuildVersion: 16B2555
Xcode Version 8.0 (8A218a)
Apple LLVM version 8.0.0 (clang-800.0.38)
Target: x86_64-apple-darwin16.1.0
Thread model: posix

Answer 1

There are few problems:
Xcode doesn't see function definitions, that's why it says 'Implicit declaration of function 'foobar' is invalid in C99'. Even despite that Xcode attempts to compile your code assuming that unknown functions will be resolved during linking phase. In the case of exit and wait it will work, but to suppress the warning you just need to include stdlib: #include <stdlib.h>.
As of gets_s you need to do some extra actions to make it work (I don't know where it comes from).
Second problem is that signature of the wait function looks like this: int wait(int *), while you are not giving any parameters to it. Simply add 0 or NULL if you don't need to get exit code from a child process back.