I write some functions to use dinamic arrays in c, without the problem of pointers ecc. , and now that i write enough code to use it properly, i want to encapsulate all this functions in a library.

Anyway in many of this function i use memcpy() method of the string.h.

So my question is:

• Need i to include string.h in the .h file?

• if i use string.h in the application where i will include my own library, will it be compilated two times?

• is there a way to optimising the compilation?

There aren't some guides about it online, and if there are, they are so ambiguos and confusing.

I found something about the ifdef but i don't really understand how and why use it.

Can somebody give me an example of the header file with a similar scenario, or at least a tutorial for writing header files?

This is the first time that i try to write a library in c, so all tips will be appreciate.

CodePudding user response：

Your header file will be shared between the final application and your library. Therefore, the best place to include <string.h> is your header file.

Do not worry about system or standard headers being included more than once. They normally have protective #ifdefs which take care of including the code only once.

As a good practice you can also insert a custom #ifdef in your header. For instance, your header file would look like this:

/* Beginning of header file */
#ifndef ALEX_XXX_HEADER

#define ALEX_XXX_HEADER

/* Your header constants, prototypes, etc. here */

#endif
/* End of header file */

In this way, the compiler will first check whether _ALEX_XXX_HEADER has been defined. If it hasn't, it means it is the first time it hits this file. Then, it defines your header macro _ALEX_XXX_HEADER and processes all the code in the header.

If the header is included more than once, the next time the compiler finds the #ifndef line, it will skip the entire #ifndef clause. In other words, it will skip the entire header file. As a result, the header code will be included once only.