Variable scope in old C

SuPete

Pete

22 posts

#4921

Variable scope in old C

8 years, 6 months ago Edited by Pete on October 1, 2015, 6:50am Reason: Code formatting

I am working on a project where there is a lot of old code written for Windows.

On several places in the code i run in to the following situation.

for(int i=0;i < 10; i++)
{
    // does stuff
}

// a couple of lines

for(i=0; i < 20; i++)
{
    // does stuff with variable i that was declared in the previous for-loop
}

The compiler throws an error at me saying i is not declared for the second for-loop. I am willing to agree with the compiler.

But since this code has been around for a long time I am suspecting that this actually worked at some time.

My question is if this was a thing in old-style C or C++? For me it looks really odd.

Sorry for getting off the topic of Handmade hero in this post I just thought this was a good forum to ask this type of question.

Also, love this project and I want to thank Casey for clarifying so much stuff.

AsafG

Asaf Gartner

64 posts / 2 projects

Handmade Network Staff

#4922

Variable scope in old C

8 years, 6 months ago

That used to be valid code. That's why you can see Casey doing for loops like this in some early videos:

1
2
3

{for(int i = 0; i < 10; ++i)
{
}}

That way the `i` is guaranteed not to stick around after the for loop.

mmozeiko

Mārtiņš Možeiko

2561 posts / 2 projects

#4923

Variable scope in old C

8 years, 6 months ago Edited by Mārtiņš Možeiko on September 30, 2015, 5:13pm

It was valid code only with Visual Studio. In C that was never a valid code.
Not sure how far back it goes, but Visual Studio 6 allowed that. Starting with next version of Visual Studio (2005) they disabled this behavior by default.

You can still enable old behavior by using /Za, /Zc, /Zc:forScope compiler argumnets - https://msdn.microsoft.com/en-us/library/84wcsx8x.aspx Even in latest Visual Studio 2015.

Another "trick" some people used to avoid this behavior in old VS6 was to redefine for keyword:

1	#define for if (0) {} else for

This forces compiler to put for variable in scope of else statement and it doesn't go outside of it.

SuPete

Pete

22 posts

#4924

Variable scope in old C

8 years, 6 months ago

Thank you for the clear answers. Now I know why it looks this way and that i can make my changes without worrying to much that i brake something else.