CODEWITHSUNDEEP
cgccclang
CupOfGreenTea
CupOfGreenTea

Reputation: 409

Why is there a need to link with `printf.o` if it's already defined inside `stdio.h`?

As far as I understand when we include stdio.h the entire file is copied into the text of our program.(basically we prepend it) Then when we do a function call for printf() why does it have to be linked first?

Is it that stdio.h contains just the definitions of those functions and the compiler finds the compiled executable object file for the function that we invoke for example printf().

I've read about this in a few places but still kinda not clear.

Upvotes: 1

Views: 442

Answers (2)

Luis Colorado
Luis Colorado

Reputation: 12668

Nope. printf() is included in libc.so (this is where the printf() function resides), which is the C standard library. The compiler includes automatically -lc as option, when it calls the linker, so you don't need to add that option. Only in case you link your object files calling the linker ld directly, is when you need to include the option yourself (and some other files that form the C runtime, the linker doesn't know that you are linking a C source program, so it doesn't know what files to link with your modules, but the compiler does) See the documentation of the compiler you use, or just use the -v option when building the executable, to see the command line the compiler uses to call the linker, and you will see all the objects and libraries the compiler requires for every C program.

Upvotes: 0

David Grayson
David Grayson

Reputation: 87416

Header files like stdio.h generally just contain a declaration that defines the name of the function, the types of its arguments, and its return value. This is enough for the compiler to generate calls to the function, but it is not a definition. The actual code that implements the function is going to be in a library (with an extension like .a or .o or .lib).

Upvotes: 3

Related Questions