Local Variables anomaly!!
 

I recently came across a piece of code that caught my attention:

main(){

char *s;
char fun();

s=fun();
printf("%s",s);
}
char *fun(){
char buffer[30];
strcpy(buffer,"Hello");
return buffer;
}
Which gives an error: buffer is a local variable and it doesn't exist in main function......
But if I run a code like:

main(){
int i;
i=new_fun();
printf("%d",i);
}

int new_fun(){
int temp;
temp= 10;
return temp;
}

It runs just fine...
Why is the anomaly in both codes present..??

The ANSI standard states that main() returns an integer. buffer is not integer.

Since arrays are returned by reference, when you return an array you are only returning a reference to it. If the array was declared within the function then its memory would have been released by the time you use its reference outside the function.

I would also point out that your 2 versions of code are not similar as the second is not using arrays

Thanx grail...yeah I almost got it..But are integers by default returned by value?...doesn't it always involve the overhead of extra memory space..??

Hi -

As you can guess, this function will return "4".

Parameter "a" was definitely "passed by value" ...
... and function "myfunc()" definitely returns an "int" ...
... but I wouldn't see the value 4 was "returned by value". I'd merely say "function 'myfunc ()' returned an int".

PS:
This applies equally to C and C++.

The big differences here are:
1) C++ absolutely *requires* you to specify the return value type (or specify "void" if there is *no* return value), classic "C" would default to "return int". You should *always* explicitly declare your return value, in *both* C and C++. Whether you get a compile error or not :)

2) C++ would allow either/both the parameter and/or return value to be a reference ("&"). C doesn't support references (at least not the last time I looked). Pointers: yes. References: no.

'Hope that helps .. PSM

PPS:
No, there's no "extra memory space". An integer return value is usually copied to a register (for example, "eax" for an Intel CPU).