What is the Scope of a funtion return? In this example
Code:int main() { int a,b; a=5; a = foo(a); printf("%d", a); } int foo(int x) { x = x + 2; return x; }
It appears that if the function foo is passing by value but the purpose is to re value a in main. How is this possible if not by reference?
Thanks in advance
The output there is 7, so I'm not sure what you are confused by.
However, here's a pass by reference version:
The output is also 7.Code:#include <stdio.h> void foo(int *x) { *x = *x + 2; } int main() { int a,b; a=5; foo(&a); printf("%d", a); }
You might want to read this, it's incomplete but covers what you are interested in here I think:
http://206.251.36.107/programming/passbyvalue.mhtml
C programming resources:
GNU C Function and Macro Index -- glibc reference manual
The C Book -- nice online learner guide
Current ISO draft standard
CCAN -- new CPAN like open source library repository
3 (different) GNU debugger tutorials: #1 -- #2 -- #3
cpwiki -- our wiki on sourceforge
I believe he's confused because he thought the variable x, being local, would not actually return anything valid to main().
Which it did, of course.
Author Horton in "Beginning C Programming", described returning local variables this way:
"The golden rule is to NEVER return the address of a local variable".
As long as the local variable's *value* is caught immediately by another variable, you're OK. (as you have shown with x, being "caught" by a, in main() ).
If you returned a pointer however, you would inevitably use that pointer (dereference it), later in the program, and then you'd be *toast*, since x would no longer exist.
I was reading the great tutorial that MK27 recommended and got to thinking on the topic of passing variables and realized that I have not been exposed to any thinking in the way of the scope variables being passed from a function as a return. I realize now that the topic includes "returning" and this may make a difference. It appears that when returning a variable the rules are different. The copy/pointer thing is not working the same in this scenario. Would the correct topic be "Scope of Returns from Functions"?
Thanks for the replies
Last edited by theKbStockpiler; 06-16-2010 at 10:35 AM.
The scope is the same. The function is making a copy of the variable and returning it. So basically its data is copied over, but the variable inside the function is destroyed.
Originally Posted by Adak
