c fopen write append code example

Example 1: fopen c

FILE *fopen(const char *filename, const char *mode)

Example 2: append to file open c

char inputChar = 'h';
int fdDataTxt = open("./data.txt", O_WRONLY | O_APPEND | O_CREAT, 0666);  
write(fdDataTxt, &inputChar,1);