Thread: How to return a string from a function

Hi, everyone. I have a function that optionally produces up to 3 strings. Each string has a maximum length, which is unique to each string.

I can do it like this:

Code:

void producestrings (char (*sz1)[a], char (*sz2)[b], char (*sz3)[c]);

char sz1[a];
char sz2[b];
char sz3[c];

producestrings (&sz1, &sz2, &sz3);

in which case the function risks wasting some memory if the strings are not as long as they could be. Or I can do this:

Code:

bool producestrings ( char **sz1, char **sz2, char **sz3);

char *sz1;
char *sz2;
char *sz3;

producestrings(&sz1, &sz2, &sz3);

in which case the function allocates memory with malloc(), which must be free()d by the calling function. This means manual memory handling and the risk of forgetting to free() the memory.

Which is better?

TIA,
Richard

Originally Posted by Richardcavell

Which is better?

That's probably a subjective question. The first one will trade memory to save CPU cycles because it doesn't have to malloc(), but the other will save memory by deciding what it needs at run-time, but waste CPU cycles allocating that memory.

If your function is going to be called lots of times, go for the first one. If it's going to be called to create huge strings (i.e. on a desktop machine you'd be measuring them in megabytes) go for the second one. If neither of these apply, go for whichever one's easiest for the programmer (this is personal preference but I'd go for the first one). If both apply then go for the one that's easiest for the programmer and see if this works in practice - if not, think about changing it.

Originally Posted by laserlight

it is more typical to pass a pointer to the first character rather than a pointer to the array itself.

Notice, however, that the method I've described ensures that the array is exactly the right size.

Richard