Have macro 'return' a value

Question

I\'m using a macro and I think it works fine -

#define CStrNullLastNL(str) {char* nl=strrchr(str,\'\\n\'); if(nl){*nl=0;}}

So it works to zero out the last

Answer 1

If you really want to do this, get a compiler that supports C++0x style lambdas:

#define CStrNullLastNL(str) [](char *blah) {char* nl=strrchr(blah,'\n'); if(nl){*nl=0;} return blah;}(str)

Although since CStrNullLastNL is basically a function you should probably rewrite it as a function.

Answer 2

I gave +1 to Mike because he's 100% right, but if you want to implement this as a macro,

char *CStrNullLastNL_nl; // "private" global variable
#define nl ::CStrNullLastNL_nl // "locally" redeclare it
#define CStrNullLastNL( str ) ( \
    ( nl = strrchr( str, '\n') ), /* find newline if any */ \
    nl && ( *nl = 0 ), /* if found, null out */ \
    (char*) nl /* cast to rvalue and "return" */ \
OR  nl? str : NULL /* return input or NULL or whatever you like */
)
#undef nl // done with local usage

Answer 3

to return value from macro:

bool my_function(int a) {
    if (a > 100)return true;
    return false;
}
bool val = my_function(200);

#define my_macro(ret_val,a){\
    if(a > 100 ) ret_val = true;\
    ret_val = false;\
}
bool val; my_macro(val, 200);