C post increment not working on a pointer but addition assignment does-CodePudding

I have a simple function to count words and characters taking two pointers and the file stream:

void countWordsAndChars(FILE *stream, int *pWordCount, int *pCharCount)
{
    int ch = getc(stream);
    while (ch != EOF)
    {
        if (!isspace(ch) && ch != '\n')
        {
            *pCharCount  ; // Does not work
            *pCharCount  = 1; // Works
        }
        else 
        {
            *pWordCount  ; // Does not work
            *pWordCount  = 1; // Works
        }
        ch = getc(stream);
    }
}

If I use the autoincrement operators (*pWordCount ) it doesnt work. But if I use the addition assignment (*pWordCount = 1) it does.

I'm coming from the web dev world and am pretty new to C. Please explain why.

Thanks.

CodePudding user response：

They are different:

*pCharCount ; equals to *(pCharCount ) so it dereferences the pointer (which does not do anything) and then increases the pointer.

*pCharCount = 1; increases the object referenced by the pointer.

If you want to use postincrement operator you need to: (*pCharCount) ;

CodePudding user response：

The answer should become clear by looking at the table of operator precedence.

As you can see in the table, the postfix operator has higher priority than the indirection operator *. (Please do not confuse the postfix operator with the prefix operator, as they have different priorities.)

Therefore, the expression

*pCharCount

is equivalent to:

*(pCharCount  )

On the other hand, the * operator has higher priority than the = operator, so the expression

*pCharCount  = 1

is equivalent to:

(*pCharCount)  = 1