"Bad to the Bone" older source...

#include <stdio.h>
#include <stddef.h>
#include <time.h>

#define OUTPUT ”out”
#define INPUT ”in”

int main (void) { // define file handles
  FILE * ofp_export , * ofp_gpio44_value , * ofp_gpio44_direction ;

// define pin variables
int pin_number = 44, logic_status = 1; char * pin_direction = OUTPUT;

// define pin variables
int pin_number = 44, logic_status = 1;
char* pin_direction = OUTPUT;

// establish a direction and value file within export for gpio44
  ofp_export = fopen("/sys/class/gpio/export", "w");
  if(ofp_export == NULL) {printf("Unable to open export.\n");}
    fseek(ofp_export, 0, SEEK_SET);
    fprintf(ofp_export, "%d", pin_number);
    fflush(ofp_export);

// configure gpio44 for writing
  ofp_gpio44_direction = fopen("/sys/class/gpio/gpio44/direction", "w");
  if(ofp_gpio44_direction == NULL){printf("Unable to open gpio44_direction.\n");}
    fseek(ofp_gpio44_direction, 0, SEEK_SET);
    fprintf(ofp_gpio44_direction, "%s", pin_direction);
    fflush(ofp_gpio44_direction);

// write a logic 1 to gpio44 to illuminate the LED
  ofp_gpio44_value = fopen("/sys/class/gpio/gpio44/value", "w");
  if(ofp_gpio44_value == NULL) {printf("Unable to open gpio44_value.\n");}
    fseek(ofp_gpio44_value, 0, SEEK_SET);
    fprintf(ofp_gpio44_value, "%d", logic_status);
    fflush(ofp_gpio44_value);

// close the files
  fclose(ofp_export);
  fclose(ofp_gpio44_direction);
  fclose(ofp_gpio44_value);

  return 1;
}

From a book, "Bad to the Bone."