CODEWITHSUNDEEP
cgccinlinec99
Doug
Doug

Reputation: 35146

How do I use but not expose an inline function in a c99 library?

I'm writing a library in C99, and there are some parts of the library that would benefit significantly from the use of a macro / inline function. Inline functions are a better fit for my library.

However, very specifically I do not want to externally expose these inline functions.

Everything appears to work, but when I link against the library to create an executable I get the error: "undefined reference to `na_impl_gfx__draw'"

I have reproduced the problem to a minimal test case which does exactly what I do:

lib.h:

void somefunc();

lib.c:

#include <stdio.h>
#include "lib.h"

inline void someinline(char *value);

void somefunc() {
  someinline("Hi!");
}

inline void someinline(char *value) {
  printf("%s\n", value);
}

main.c:

#include "lib.h"
int main(int argc, char *argv[]) {
  somefunc();
}

Now we compile:

doug@Wulf:~/test$ gcc -c -std=c99 lib.c
doug@Wulf:~/test$ gcc -c -std=c99 main.c
doug@Wulf:~/test$ gcc -std=c99 lib.o main.o
lib.o: In function `somefunc':
lib.c:(.text+0xe): undefined reference to `someinline'
lib.c:(.text+0x1a): undefined reference to `someinline'
lib.c:(.text+0x26): undefined reference to `someinline'
collect2: ld returned 1 exit status

It would appear that when compiling the library, the inline function is not being substituted into the object code for the function somefunc() in lib.h

Why?

The inline function is not externally visible. I would expect that when the library is compiled, the inline function is inlined into the function, just like the macro is (Nb. using only a macro this code compiles file).

What am I doing wrong? Or is this a restriction of inline functions?

Upvotes: 3

Views: 2375

Answers (2)

Jens Gustedt
Jens Gustedt

Reputation: 78923

[Sorry for kicking in as lately, you should have tagged your question with C and not only C99.]

I think with your question you are completely on the wrong track. Inline functions only make sense when you put them in a ".h" file. The whole concept is about making the function definition visible to all callers.

If you'd do so you should just put the definition (with the inline) in the header and an external declaration (with extern inline) in one compilation unit.

If you just want to have functions put in place in your "lib.o" compilation unit, forget about all that inline or static and let the compiler do that for you. gcc does that if you switch on optimization:

`-finline-small-functions' Integrate functions into their callers when their body is smaller than expected function call code (so overall size of program gets smaller). The compiler heuristically decides which functions are simple enough to be worth integrating in this way.

 Enabled at level `-O2'.

Upvotes: 4

Lawrence Woodman
Lawrence Woodman

Reputation: 1444

The reason that you can't see the inline function in the same source file is that you haven't made them static.

All you need to do is make the prototype static with:

inline static void someinline(char *value);

and the function definition static with:

inline static void someinline(char *value) {
  printf("%s\n", value);
}

Upvotes: 5

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