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function arguments and returning, how to set my code out!

SuperStinger (84)
Hi all!

I have a struct that i want to return from a function, but i think it is a bit inefficient to return a really big struct, so i want to return its pointer.

Can i create the struct variable inside the function and then return its pointer, or would the pointer be dangling and left leading to nothing.

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//Struct to hold a bmp of a font and information about it, offsets always start from 32 ( space in ascii )
typedef struct
{
	//This is the actual bitmap of ascii characters that we will blit from
	SDL_Surface* bmp;

	//The array that holds all the symbols, the array size is 94 to go from ascii space ( 32 ) to the tidle ( 126 )
	struct symbol[94];
} font;

font* loadFont ( char* fileName )
{
	font returnStruct;

	//Blah blah load struct stuff, struct.blah = 1

	//--Am i doing this right?--
	return &returnStruct;
}


How would i approach this?

Also, would i be able to modify a function argument, is there anything wrong with that?

So if created the struct variable outside of the function ( in main ) and then passed it as an argument, which was a pointer, then i modify that?

Many thanks, SuperStinger
closed account (zb0S216C)
Never return the address of automatic storage. The safer option is to make a static pointer within the function and return that instead.

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Font *LoadFont( char *FileName_ )
{
    static Font *Font_;
    // Load the font...
    return( Font_ );
}

This has it's drawbacks, but does ensure that "Font_" remains valid until the program ends. With each call to the function, the address pointed-to by "Font_" can change. This is the safest way of returning the address of storage that's declared within a function's scope. Note that static storage declared within a function scope remains even if the function is not currently being executed.

Wazzak
Last edited on
closed account (1yR4jE8b)
Your loadFont method should probably be a member function of the font struct.

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//Struct to hold a bmp of a font and information about it, offsets always start from 32 ( space in ascii )
typedef struct
{
	//This is the actual bitmap of ascii characters that we will blit from
	SDL_Surface* bmp;

	//The array that holds all the symbols, the array size is 94 to go from ascii space ( 32 ) to the tidle ( 126 )
	struct symbol[94];

    void loadFont ( char* fileName )
    {
	//Blah blah load struct stuff, struct.blah = 1
    }
} font;
SuperStinger (84)
thanks for your responses

@darkestfright: from the loadFont function that i would put in the typedef struct, how would i access the variables inside the struct ( i.e bmp and symbol )

EDIT: ive tried various things by putting the function inside the typedef, but it gives me errors, i dont know how to do this, can someone show me please? many thanks

EDIT2: dont worry, im writing in pure C, not C++, so it doesnt like that, ill just make functions outside of the typedef, thanks for your help
Last edited on
JLBorges (13770)
> but i think it is a bit inefficient to return a really big struct,
> so i want to return its pointer.

No, it is not. Every current mainstream compiler implemts NRVO.
http://en.wikipedia.org/wiki/Return_value_optimization
http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/
closed account (1yR4jE8b)
dont worry, im writing in pure C, not C++, so it doesnt like that


You should be more clear about that in the future then.
kev82 (323)
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int loadFont ( char* fileName, font *f )
{
	//Blah blah load struct stuff, f->blah = 1

	return 1; //if loading succeeded 
}


font f;
loadFont("font name", &f); //should check for failure here
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