Question

char* timecompare(){
    char time[8];
    snprintf(time,8,"%i:%02i",hour(),minute());
    return time;
}

char* timefeed = "8:0";

if (strcmp(timecompare(), timefeed) == 0){
    Serial.println("hello"); 
}

I have this as my code when timecompare() and timefeed are both equal it is not printing hello? I this a pointer problem? I instead of comparing timecompare() with timefeed I compare timecompare() with “8:0” then the loop works… Is this a problem with the timefeed variable?

Answer 1

You are returning a stack allocated variable, time, from timecompare(). This is illegal since stack allocated memory is only valid in the function in which the variable is declared.

Instead you need to return a heap allocated string. Your compiler should be warning you of this. You could write it like this:

char* timecompare(){
    char* time = malloc(8);
    snprintf(time,8,"%i:%02i",hour(),minute());
    return time;
}

Remember to free() the memory after you are finished with it.