Question

I have a sorted array of some indeterminate number of variables and counts thereof. I need to build a string like so:

Attribute[0]: p=2, e=8

My issue is the array is actually a pointer, and I don’t want to use a loop of fixed length, so the only solution I see is to use an array pointer.

void printArray(Node_ptr node){
    int count=0; //character count
    char *temp= node->attributes; //duplicate attribute array

    char cur; //current char
    char *outputCat= emalloc(150); //concatenate counts to a single string

    strcpy(outputCat, "Attribute %d counts are: ");
    qsort(temp, lineCount, sizeof(char), compare); //sort the array

    while ((temp) != NULL){
        cur= *temp;
        ++temp;
        if (strcmp(&cur, temp)==0) //if characters are same
            count++; 
        else { //build reporting string
            strcat(outputCat, &cur);
            strcat(outputCat, "= ");
            sprintf(outputCat, "%d  ", count);
            count=0;
        }
    }
    free(outputCat);
}

The issue here is strcmp(&cur, ++temp)==0 is returning false every time, even when I see their values in the debugger. Because of this, the else conditional is constantly being built up and throws a segfault after a number of iterations.

Two questions:

1- What can make strcmp return non-zero even when identical values are entered?
2- What can I do to fix the code?

Answer 1

In your line:

strcmp(&cur, temp)

cur is a char declared locally, and therefore, &cur is just some location on the stack, and rather meaningless in this context.

I believe you mean to check if the current-character cur is the same as the next character *temp.
This would look like:

if (cur == *temp) //if characters are same
    count++; 

Next, I would look at massively simplify your output section:

sprintf(outputCat, "%c = %d", *cur, count);  // e.g.   "e = 8"
count=0;

And finally, I doubt your loop will ever terminate, as it continues to do temp++, while temp != NULL.
I believe you intend to check the VALUE stored at the pointer temp.
*temp should be properly checked against ‘\0’, instead of NULL.
(\0 and NULL happen to have the same value, but they should not be treated the same semantically)

while (*temp != '\0'){

P.S. Your simple, but excellent comment “// if characters are same” was extremely helpful for me to understand your code. This is an excellent case of short, meaningful comments being INVALUABLE. Thank you.

---

(Hopefully final edit)
In total, the changes I recommend look like:

void printArray(Node_ptr node){
    int count=0; //character count
    char *temp= node->attributes; //duplicate attribute array

    char cur; //current char
    char *outputCat= emalloc(150); //concatenate counts to a single string

    strcpy(outputCat, "Attribute %d counts are: ");
    qsort(temp, lineCount, sizeof(char), compare); //sort the array

    while (*temp != '\0'){
        cur= *temp;
        ++temp;
        if (cur == *temp) //if characters are same
            count++; 
        else { //build reporting string
            sprintf(outputCat, "%c = %d", *cur, count);  // e.g.   "e = 8"
            count=0;
        }
    }
    free(outputCat);
}

How’s that work out for you?