Issue
How does a compiler find out which dynamic link library will be used in my code, if I only include headers-files, where is not describe it?
#include <stdio.h>
void main()
{
printf("Hello world\n");
}
There is I only include
stdio.h
and my code is used
printf function
How it is known, in headers-files prototypes , macros and constant are described, but nothing about in which file "printf" is implement. How does then it works?
Solution
When you compile a runnable executable, you don't just specify the source code, but also a list of libraries from which undefined references are looked up. With the C standard library, this happens implicitly (unless you tell GCC -nostdinc), so you may not have been consciously aware of this.
The libraries are only consumed by the linker, not the compiler. The linker locates all the undefined references in the libraries. If the library is a static one, the linker just adds the actual machine code to your final executable. On the other hand, if the library is a shared one, the linker only records the name (and version?) of the library in the executable's header. It is then the job of the loader to find appropriate libraries at load time and resolve the missing dependencies on the fly.
On Linux, you can use ldd to list the load-time dependencies of a dynamically linked executable, e.g. try ldd /bin/ls. (On MacOS, you can use otool -L for the same purpose.)
Answered By - Kerrek SB Answer Checked By - Candace Johnson (WPSolving Volunteer)
