由于“'isblank'未在此范围内声明”错误，Mingw无法编译

Question

I try to compile & link the following program with mingw. When I use the default version it works well. But when I use c++11 version it doesn't compile and gives me the following error newfile.cpp:22:18: error: 'isblank' was not declared in this scope . for testing the following program it's enough to call the _isblank function in main.

For compiling the Netbeans 8.0.2 uses g++ -c -g -Wall -std=c++11 -MMD -MP -MF "build/Debug/MinGW_1-Windows/newfile.od" -o build/Debug/MinGW_1-Windows/newfile.o newfile.cpp .

The mingw version is 4.8.1 and everything is configured well(Default).

I tried by adding/removing namespace std. The problem seems to be in cctype header! But I wonder how to solve it. The project will have to be compiled with g++ on linux! Will these problems remain?

#include <cstdlib>
#include <cctype>
#include <fstream>
#include <sstream>
#include <string>
#include <iostream>
#include <map>
#include <functional>
#include "newfile.h"

using namespace std;
conf_info_t CONF_INFO;

#define CONF_FILE_ADDRESS "confs.txt"
//
//typedef std::map<std::string, std::function<void (const std::string&)>> confMap_t;
//confMap_t confMap;

int _isblank(int c){
    return isblank(c);
    //return c == ' ' || c == '\t';
}

Answer 1

In my version of GNU library the declaration of isblank in <ctype.h> header is protected by some conditional compilation directives, which nevertheless should make this function available in C++.

However, in <cctype> header this function is is separated from all other declarations and given a special treatment for some reason. It is only made available in namespace std if macro _GLIBCXX_USE_C99_CTYPE_TR1 is defined. This is what it looks like inside <cctype>

#if __cplusplus >= 201103L

#ifdef _GLIBCXX_USE_C99_CTYPE_TR1

#undef isblank

namespace std
{
  using ::isblank;
} // namespace std

#endif // _GLIBCXX_USE_C99_CTYPE_TR1

#endif // C++11

I don't know what the purpose that _GLIBCXX_USE_C99_CTYPE_TR1 macro is supposed to serve. In my GCC installation this macro is defined, which makes isblank available in my case.

You might want to check what your <cctype> looks like and see if something like that is happening on your side as well.

Answer 2

It worked when I undefined STRICT_ANSI in the translation unit adding -U__STRICT_ANSI__ to the compiler options. But I wonder which part of my program violates C++ standards.

It should have been compiled in this way:

g++ -U__STRICT_ANSI__   -c -g -Wall -std=c++11 -MMD -MP -MF "build/Debug/MinGW_1-Windows/main.o.d" -o build/Debug/MinGW_1-Windows/main.o main.cpp