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Home » Tip Bank » C++
Language: C++
Expertise: Intermediate
Aug 27, 2001

Fix MSVC++'s "for"


MSVC has a small, but annoying bug with the scope of variables defined in "for" loops. For example, the following fragment is valid C++, but will not compile on MSVC:
 
for(int i=0; I<10; i++) {
    DoSomeThing();
}

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

MSVC will complain about the second for loop, because the variable "i" is defined as if it were scoped just outside of the first "for" loop.

What follows is a quick one liner to put at the top of your file, (or even better, in your MSVC-specific header files, since everyone is, of course, targeting multiple platforms and compilers):
 
#define for if(false) {} else for

With this code, "for" loops will have the semantics that they should, with one small exception: should you type/syntax err badly enough to have an "else" clause right after your "for" loop, the compiler will not catch the error. But I've never heard of this happening anyway.
Prashant Mhatre
 
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