Difference between WIN32 and other c string [duplicate]

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Difference between WIN32 and other c string

I got this code inside a small program to read a file

 #ifdef WIN32  

        unsigned char *buffer = (unsigned char *)alloca((unsigned int)ui.length);
 #else

         unsigned char buffer[ui.length];
 #endif

Can anybody tell me , why pointer used for win32 platform and character array for other platfo开发者_Go百科rm?

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The code intended to declare an array of length not known at compile time. It was likely written with the assumption that C++ compilers for Windows targets don't support declaring such arrays (for example, Visual C++ doesn't support that). So when compilation is done for Windows targets alloca() function is used to achieve the same effect.

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I guess that the compiler used for WIN32 compilation does not support C99 variable length array declarations.