Useful C tricks and code samples.

Posted: August 5, 2015. At: 11:21 PM. This was 2 years ago. Post ID: 8290
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How to define a string and print it out with the printf() function.

#include <stdio.h>
 
/* Defining a global string. */
 
#define hi "Hello Sire."
 
int main(void)
{
   /* Printing out the string. */
   printf("%s\n", hi);
 
   return 0;
}

How to run the /bin/sh executable with some C code.

#include <stdlib.h>
#include <unistd.h>
 
int main(void)
{
        execve("/bin/sh", NULL, NULL);
        return 0;
}

When no parameters are passed to a C program, display a menu.

	if (!argc || !argv[1]) {
		char *myarg;
		myarg = argv[0];
		printf("%s Usage:\n--datetime - Date & Time.\x2e\n" \
		"--uname1 - Kernel Information\x2e\n" \
		"--uname2 - Information on memory & processes\x2e\n" \
		"--fortune - View a fortune cookie.\x2e\n" \
		"--about - The Readme for this program\x2e\n\n" \
		, myarg);
	}

Print the current time and date.

void DateTime()
{
	struct tm *ptr;
	time_t tm;
	char str[60];
	tm = time(NULL);
	ptr = localtime(&tm);
	strftime(str, 100, "%A %d %B %Y. %H:%M:%S %Z.", ptr);
	printf("\n\n%s\n\n", str);
}

How to define and use a function as well as getting input from the console.

#include <stdio.h>
#include <string.h>
 
#define MSG "World"
 
int goku(void) {
	printf("Hello %s.\n", MSG);
	return 1;
}
 
int main(int argc, char **argv) {
 
	char *name;
 
	name = argv[1];
 
	if (strlen(name) < 5) {
		printf("Name too short.\n");
	}
	goku();
	printf("%s\n", name);
	return 0;
}

Here is a simple C program for printing a verbose time and date.

#include 	/* For time function (random seed). */
#include       /* For extra functions. printf().   */
#include      /* For getenv();                    */
 
#define format "The time and date is: %A %d %B %Y. The time is: %H:%M:%S, %Z."
 
int print_time(void) {
	struct tm *ptr;
	time_t tm;
	char length[60];
	tm = time(NULL);
	ptr = localtime(&tm);
	strftime(length, 100, format, ptr);
	printf("%s\n", length);
}
 
int main(void)
{
	print_time();
	return 0;
}

Simple Hello World program.

int main() {
	write(1, "Hello World\n", 14);
}

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