putting function definitions in header files

Question

If you want to put function definitions in header files, it appears there are three different solutions:

1. mark the function as inline
2. mark the

Answer 1

As far as I know, only inline and template functions can be defined in header files.

static functions are deprecated, and functions defined in an unnamed namespace should be used instead (see 7.3.1.1 p2). When you define a function in an unnamed namespace in a header, then every source code including that header (directly or indirectly) will have an unique definition (see 7.3.1.1 p1). Therefore, functions should not be defined in the unnamed namespace in header files (only in source files).

_{The standard referenced are from the c++03 standard.}

EDIT:

Next example demonstrates why functions and variables shouldn't be defined into unnamed namespace in headers :

ops.hpp contains:

#ifndef OPS_HPP
#define OPS_HPP
namespace
{
int a;
}
#endif

dk1.hpp contains:

#ifndef DK1_HPP
#define DK1_HPP
void setValue();
void printValue();
#endif

dk1.cpp contains:

#include "dk1.hpp"
#include "ops.hpp"
#include 

void setValue()
{
    a=5;
}
void printValue()
{
    std::cout<

dk.cpp contains :

#include "dk1.hpp"
#include "ops.hpp"
#include 

int main()
{
    // set and print a
    setValue();
    printValue();

    // set and print it again
    a = 22;
    std::cout<

Compile like this:

g++ -ansi -pedantic -Wall -Wextra dk.cpp dk1.cpp

and the output :

5
22
5

ops the variable a is different for the source file dk1.cpp and dk.cpp