Pipe output of any command line program to buffer in C.

cmdl.c

#ifndef CMDL_H_
#define CMDL_H_

#ifdef _WIN32
#include <windows.h>

static const char *cmdl_errlist[] = {
	"No Error.",
	"CreatePipe() failed: could not create a pipe.",
	"CreateProcessA() failed: could not create child process.",
	"CloseHandle() failed: could not close write end of pipe.",
	"CloseHandle() failed: could not close read end of pipe.",
	"CloseHandle() failed: could not close thread.",
	"CloseHandle() failed: could not close process.",
};
static const unsigned int cmdl_errlist_size = sizeof(cmdl_errlist)/sizeof(cmdl_errlist[0]);
static unsigned int cmdl_errno = 0;

const char *cmdl_strerror(void) {
	if (cmdl_errno >= cmdl_errlist_size) return "Invalid Error.";
	
	return cmdl_errlist[cmdl_errno];
}

int cmdl_win32(char *command, char *buffer, int size) {
	HANDLE pipefd[2];
	STARTUPINFOA si = {0};
	PROCESS_INFORMATION pi = {0};
	SECURITY_ATTRIBUTES sa = {0};
	DWORD bytes;

	sa.nLength = sizeof(sa);
	sa.lpSecurityDescriptor = 0;
	sa.bInheritHandle = 1;
	
	if (!CreatePipe(&pipefd[0], &pipefd[1], &sa, 0)) {
		cmdl_errno = 1;
		return 0;
	}
	
	si.cb = sizeof(si);
	si.hStdOutput = pipefd[1];
	si.dwFlags = STARTF_USESTDHANDLES;
	
	if (!CreateProcessA(NULL, command, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi)) {
		cmdl_errno = 2;
		return 0;
	}
	
	if (!CloseHandle(pipefd[1])) {
		cmdl_errno = 3;
		return 0;
	}
	
	while (size) {
		if (!ReadFile(pipefd[0], buffer, size, &bytes, NULL)) break;
		buffer += bytes;
		size -= bytes;
	}
	
	if (!CloseHandle(pipefd[0])) {
		cmdl_errno = 4;
		return 0;
	}
	
	if (!CloseHandle(pi.hThread)) {
		cmdl_errno = 5;
		return 0;
	}
	
	if (!CloseHandle(pi.hProcess)) {
		cmdl_errno = 6;
		return 0;
	}
	
	return 1;
}

#define cmdl cmdl_win32
#else
#include <unistd.h>
#include <sys/types.h>

static const char *cmdl_errlist[] = {
	"No Error.",
	"pipe() failed: could not create a pipe.",
	"fork() failed: could fork the process.",
	"close() failed: could close the read end of child process.",
	"dup2() failed: could reopen the write end of child process as parent stdout.",
	"close() failed: could close the old write end of child process.",
	"execlp() failed: could not execute command.",
	"close() failed: could close the write end of parent process.",
	"read() failed: could read from child process.",
};
static const unsigned int cmdl_errlist_size = sizeof(cmdl_errlist)/sizeof(cmdl_errlist[0]);
static unsigned int cmdl_errno = 0;

const char *cmdl_strerror(void) {
	if (cmdl_errno >= cmdl_errlist_size) return "Invalid Error.";
	
	return cmdl_errlist[cmdl_errno];
}

int cmdl_posix(char *command, char *buffer, int size) {
	pid_t pid;
	int pipefd[2];
	
	if (pipe(pipefd) < 0) {
		cmdl_errno = 1;
	    return 0;
	}
	
	pid = fork();
	
	if (pid < 0) {
	    cmdl_errno = 2;
	    return 0;
	}
	
	if (pid == 0) {
	    if (close(pipefd[0]) < 0) {
			cmdl_errno = 3;
			return 0;
		}
	    
        if (dup2(pipefd[1], STDOUT_FILENO) < 0) {
            cmdl_errno = 4;
            return 0;
        }
		
        if (close(pipefd[1]) < 0) {
			cmdl_errno = 5;
			return 0;
		}
	    
	    if (execlp("sh", "sh", "-c", command, NULL) < 0) {
	        cmdl_errno = 6;
			return 0;
	    }
	}
	else {
	    if (close(pipefd[1]) < 0) {
			cmdl_errno = 7;
			return 0;
		}
		
	    if (read(pipefd[0], buffer, size) < 0) {
			cmdl_errno = 8;
			return 0;
		}	    
	}
	
	return 1;
}

#define cmdl cmdl_posix
#endif /* _WIN32 */
#endif /* CMDL_H_ */

/*///////////////////////////////////
	
		Testing:
		
///////////////////////////////////*/

#include <stdio.h>

int main() {
	char buffer[2048] = {0};

	if (!cmdl("curl github.com -L", buffer, sizeof(buffer))) {
		printf("ERROR: %s\n", cmdl_strerror());
		return 1;
	}
	
	printf("%s", buffer);
	return 0;
}