Creating a simplified version of strchr() [duplicate]

Question

Trying to create a simple function that would look for a single char in a string "like strchr() would", i did the following:

char* findchar(char* str, char c)
{
    char* position = NULL;
    int i = 0;
    for(i = 0; str[i]!='\0';i++)
    {
        if(str[i] == c)
        {
            position = &str[i];
            break;
        }
    }
    return position;
}

So far it works. However, when i looked at the prototype of strchr():

char *strchr(const char *str, int c);

The second parameter is an int? I'm curious to know.. Why not a char? Does this mean that we can use int for storing characters just like we use a char?

Which brings me to the second question, i tried to change my function to accept an int as a second parameter... but i'm not sure if it's correct and safe to do the following:

char* findchar(char* str, int c)
{
    char* position = NULL;
    int i = 0;
    for(i = 0; str[i]!='\0';i++)
    {
        if(str[i] == c) //Specifically, is this line correct? Can we test an int against a char? 
        {
            position = &str[i];
            break;
        }
    }
    return position;
}

Answer 1

Before ANSI C89, functions were declared without prototypes. The declaration for strchr looked like this back then:

char *strchr();

That's it. No parameters are declared at all. Instead, there were these simple rules:

• all pointers are passed as parameters as-is
• all integer values of a smaller range than int are converted to int
• all floating point values are converted to double

So when you called strchr, what really happened was:

strchr(str, (int)chr);

When ANSI C89 was introduced, it had to maintain backwards compatibility. Therefore it defined the prototype of strchr as:

char *strchr(const char *str, int chr);

This preserves the exact behavior of the above sample call, including the conversion to int. This is important since an implementation may define that passing a char argument works differently than passing an int argument, which makes sense on 8 bit platforms.