Dealing with returning C strings

Question

What is considered better practice when writing methods that return strings in C?

passing in a buffer and size:

void example_m_a(type_a a,char * buff,size_t buff_size)

or making and returning a string of proper size:

char * example_m_b(type_a a)

P.S. what do you think about returning the buffer ptr to allow assignment style and nested function calls i.e.

char * example_m_a(type_a a,char * buff,size_t buff_size)
{
...
return buff;
}

Answer 1

Passing a buffer as an argument solves most the problems this type of code can run into.

If it returns a pointer to a buffer, then you need to decide how it is allocated and if the caller is responsible for freeing it. The function could return a static pointer that doesn't need to be freed, but then it isn't thread safe.

Answer 2

Passing a buffer and a size is generally less error-prone, especially if the sizes of your strings are typically of a "reasonable" size. If you dynamically allocate memory and return a pointer, the caller is responsible for freeing the memory (and must remember to use the corresponding free function for the memory depending on how the function allocated it).

If you examine large C APIs such as Win32, you will find that virtually all functions that return strings use the first form where the caller passes a buffer and a size. Only in limited circumstances might you find the second form where the function allocates the return value (I can't think of any at the moment).