Is there any way to enable for(int i=0; ... in gcc without having to turn on c99 mode

Question

I've got a very big program which compiles with gcc without warnings.

If I turn on c99 mode --std=c99 on the command line, it gives a huge number of warnings and errors.

But I love the idiom for(int i=0; i<20; i++){ code }

in place of {int i; for (i=0; i<20; i++){ code }}

Is there any way to tell gcc to allow this and only this?

Alternatively, is there any way to enable c99 mode in the particular functions I'm working on? Something like

#pragma c99 on 

for(int i=0; i<99; i++)
{
    code
}

#pragma c99 off

Answer 1

It is likely that the warnings and errors are because -std=c99 requests standard-conforming C99, which means that many platform-specific functions that pollute the C99 namespace are not defined.

Instead, you should try --std=gnu99, which is the C99-equivalent to the default mode of gnu89.

Answer 2

Alternatively to use -std=gnu99 you can disable individual warnings:

-Wno-declaration-after-statement

Read info gcc:

`-Wdeclaration-after-statement (C and Objective-C only)'
     Warn when a declaration is found after a statement in a block.
     This construct, known from C++, was introduced with ISO C99 and is
     by default allowed in GCC.  It is not supported by ISO C90 and was
     not supported by GCC versions before GCC 3.0.  *Note Mixed
     Declarations::.