File Read

#define LINE_MAX   128

const char *filename = "data.dat";
char line[LINE_MAX];
FILE* file;

file = fopen(filename, "r");
if(file)
{
    while (fgets(line, LINE_MAX, file)) {
        printf("%s", line);
    }
    fclose(file);
}

File Write

const char *filename = "data.dat";
FILE* file;

file = fopen(filename, "w");
if(file)
{
    fputs("Line 1\n", file);
    fputs("Line 2\n", file);
    fputs("Line 3\n", file);
    fclose(file);
}