Producing uppercase letters without pointers

Question

I am trying to write a function, uppercase, that converts all lowercase characters in a string into their uppercase equivalents.

However, I am getting a Bus 10 error in

Answer 1

Your absolutly working with pointers without even to know it.

In your function definition

int uppercase(char source[])

char source[] is considered by the compiler as a pointer to char (char *source)

So when passing a string literal to uppercase() your just passing it's adress. Then in your function your trying to modify it which leads to undefined behaviour.

Also you can't return a whole array so you just return a pointer to it.

char *uppercase(char source[])
{
     int i;
     size_t len = strlen(source);
     char *tmp;
     tmp = malloc(len+1);
     if (tmp!=NULL){
         memcpy(tmp, source, len+1);
         for(i=0; i<len; ++i){
            if (tmp[i]>= 'a' && tmp[i]<= 'z'){
                tmp[i]= tmp[i]-'a' +'A';
            }
        }
    }
    return tmp;
}

Then:

int main(){
    char *str = uppercase("cold");
    printf("%s", str);
    free(str);

    return 0;
}

You complete code: http://ideone.com/BJHDIF

Answer 2

The reason you get a crash is that your code modifies a string literal. Characters inside string literals are placed in protected memory area, and therefore may not be changed: it us undefined behavior.

Replace this

uppercase("cold");

with this:

char cold[] = "cold";
uppercase(cold);

Now the characters of the string are placed in a modifiable area of memory, allowing you to make changes as needed.