Compiling error in C++ project with C and C++ code

I've created a C++ project where I use C and C++ codes and have some problems with headers... OK, I have 3 codes:

basicOCR.cpp

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#include "preprocessing.h"
#include "basicOCR.h"

preprocessing.c

#include <stdio.h>
#include <ctype.h>
#include <math.h>

#include "preprocessing.h"

main.c

#include <stdio.h>
#include <ctype.h>

#include "basicOCR.h"

and my 2 own header files:

basicOCR.h

#include <stdio.h>
#include <ctype.h>

preprocessing.h

#include <stdio.h>
#include <ctype.h>

Whenever I try to compile a project, it compiles basicOCR.cpp without any problems but preprocessing.c and main.c give me syntax errors in cstdlib and xstddef. I know that they are C++ libraries. I read this How to mix C and C++

and tried almost everything but it didn't work.

1>  preprocessing.c
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(19): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(19): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(19): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2061: syntax error : identifier 'abs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2061: syntax error : identifier 'atexit'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2061: syntax error : identifier 'atof'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2061: syntax error : identifier 'atoi'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2061: syntax error : identifier 'atol'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2061: syntax error : identifier 'bsearch'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2061: syntax error : identifier 'calloc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2061: syntax error : identifier 'div'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2061: syntax error : identifier 'exit'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2061: syntax error : identifier 'free'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2061: syntax error : identifier 'getenv'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2061: syntax error : identifier 'labs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2061: syntax error : identifier 'ldiv'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2061: syntax error : identifier 'malloc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2061: syntax error : identifier 'mblen'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2061: syntax error : identifier 'mbstowcs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2061: syntax error : identifier 'mbtowc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2061: syntax error : identifier 'qsort'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2061: syntax error : identifier 'rand'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2061: syntax error : identifier 'realloc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2061: syntax error : identifier 'srand'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2061: syntax error : identifier 'strtod'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2061: syntax error : identifier 'strtol'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2061: syntax error : identifier 'strtoul'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2061: syntax error : identifier 'system'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2061: syntax error : identifier 'wcstombs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2061: syntax error : identifier 'wctomb'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(32): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(34): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(34): error C2061: syntax error : identifier 'lldiv'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(34): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstddef(18): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstddef(18): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(78): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(78): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(87): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(87): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(98): error C2061: syntax error : identifier 'tr1'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(98): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(98): error C2449: found '{' at file scope (missing function header?)
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(101): error C2059: syntax error : '}'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(125): error C2143: syntax error : missing '{' before ':'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(125): error C2059: syntax error : ':'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(132): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(132): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(141): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(141): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\eh.h(27): fatal error C1189: #error :  "eh.h is only for C++!"
1>  main.c
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(19): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(19): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(19): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2061: syntax error : identifier 'abs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2061: syntax error : identifier 'atexit'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(21): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2061: syntax error : identifier 'atof'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2061: syntax error : identifier 'atoi'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2061: syntax error : identifier 'atol'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(22): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2061: syntax error : identifier 'bsearch'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2061: syntax error : identifier 'calloc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2061: syntax error : identifier 'div'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(23): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2061: syntax error : identifier 'exit'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2061: syntax error : identifier 'free'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2061: syntax error : identifier 'getenv'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(24): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2061: syntax error : identifier 'labs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2061: syntax error : identifier 'ldiv'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2061: syntax error : identifier 'malloc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(25): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2061: syntax error : identifier 'mblen'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2061: syntax error : identifier 'mbstowcs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2061: syntax error : identifier 'mbtowc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(26): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2061: syntax error : identifier 'qsort'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2061: syntax error : identifier 'rand'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2061: syntax error : identifier 'realloc'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(27): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2061: syntax error : identifier 'srand'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2061: syntax error : identifier 'strtod'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2061: syntax error : identifier 'strtol'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(28): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2061: syntax error : identifier 'strtoul'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2061: syntax error : identifier 'system'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(29): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2061: syntax error : identifier 'wcstombs'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2061: syntax error : identifier 'wctomb'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(30): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(32): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(34): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(34): error C2061: syntax error : identifier 'lldiv'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstdlib(34): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstddef(18): error C2054: expected '(' to follow 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\cstddef(18): error C2061: syntax error : identifier 'using'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(78): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(78): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(87): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(87): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(98): error C2061: syntax error : identifier 'tr1'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(98): error C2059: syntax error : ';'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(98): error C2449: found '{' at file scope (missing function header?)
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(101): error C2059: syntax error : '}'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(125): error C2143: syntax error : missing '{' before ':'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(125): error C2059: syntax error : ':'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(132): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(132): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(141): error C2143: syntax error : missing '{' before '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\xstddef(141): error C2059: syntax error : '<'
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\include\eh.h(27): fatal error C1189: #error :  "eh.h is only for C++!"

回答1:

I got that. The solution to this was to make a right click on each C code and Properties>C/C++>Advanced>Compile As and check Compile as C++ Code(/TP)

回答2:

It looks like vc use c++ headers for c code.

This does not answer the question, but why not just use C++? The only time you need C is when you want to be compatible with different versions of different compilers, which happens when you build a plug-in architecture. In this case you declare plug-in prototypes in a "SDK" header like this:

#ifndef __SDK_H
#define __SDK_H

#ifdef __cplusplus
extern "C"
    {
#endif
    __declspec(dllexport) return_type calling_convention function_name(parameters);

#ifdef __cplusplus
    }
#endif

#endif

Then you can compile your plugin.c which should contain the following:

#include "sdk.h"

return_type function_name(parameters)
     {
     /*Do stuff here*/
     }