How to write to file in C -

i have program working on start , stop servo. can issue following command command line , works. echo 2=120 > /dev/servoblaster start servo in motion. have following program

#include <stdio.h> #include <stdlib.h>  int main(void) {     file *fp;      fp = fopen("/dev/servoblaster", "w");    if (fp == null) {        printf("error opening file\n");        exit(0);   }    fprintf(fp, "2=120");    fclose(fp);    fflush(fp);     return 0; } 

but when execute nothing happens, when try echo 2=120 > /dev/servoblaster command bad input: 2=1202=120 if repeat same echo 2=120 > /dev/servoblaster command work again. if try , execute above program 3 times output when try execute echo command output bad input 2=1202=1202=120 2=120 me seems file not finished being written in program. can point out if missing something?

you need add newline after command, echo does:

fprintf(fp, "2=120\n"); 

presumably, servo's driver waits until sees newline before acting on command.