Printable View
Say I have a header file, a.h
and b.cpp, c.cpp, both needs to use this function.Code:#ifndef A_H
#define A_H
int some_util_function() {
...
}
#endif
If I compile them separately then link them, I get a multiple definitions error.
What's the standard way to fix this? (Except moving it to another .c)Code:gcc -c b.cpp
gcc -c c.cpp
gcc b.o c.o #multiple definitions
You also need to declare the function as inline using the inline keyword.
Cool! Thanks!
I thought "inline" is only a hint for the optimizer.
You need to use the 'inline' keyword when defining some_util_function. Otherwise, you'll have to compile it into it's own object file.
EDIT:
Nevermind
You thought wrong.Quote:
Originally Posted by cyberfish
"inline" has a couple of purposes.
1) an instruction to the compiler that the same function definition may be seen by multiple compilation units (eg .c files). The compiler is required to do the necessary jiggery-pokery to ensure the program is correctly built (e.g. it links) in such circumstances. The programmer is also required to ensure a different definition of the function is not introduced elsewhere (i.e. to not violate the one-definition rule).
2) a hint to the compiler that the body of the function may be placed inline at the call point, rather than using the more usual function call mechanism. In practice it is often the optimiser that accepts, or ignores, that hint but it doesn't have to be.
If the compiler doesn't inline the function, it is obliged to accept the source code and produce a compileable program as if it had inlined the function. We can't have code suddenly fail to link because the compiler chose not to inline on any particular day. And so it also serves to prevent multiple definitions.Quote:
Originally Posted by cyberfish