修复奇怪的“％a”格式行为与g ++ 4.9.1？ [英] Fix for bizarre "%a" format behavior with g++ 4.9.1?

问题描述

编译器：64位MinGW G ++ 4.9.1，来自Nuwen发行版，在Windows 8.1下。

代码：

  #ifdef INCLUDE_IOSTREAM 
＃include< iostream> 
 #endif 
 #include< stdio.h> // :: snprintf 
 #include< stdlib.h> // EXIT_SUCCESS，EXIT_FAILURE 
 #include< stdexcept> // std :: exception 
 $ b $＃#ifdef snprintf 
＃error snprintf被定义为宏
 #endif 
 
 #ifdef _MSC_VER 
 auto const snprintf = _snprintf; 
 #endif 
 
 void test（double const value，int const precision）
 {
 char buffer [34]; 
 snprintf（buffer，sizeof（buffer），％。* a，precision，value）; 
 printf（％.3f与％2d数字的十六进制：％s \ n，数值，精度，缓冲区）; 
} 
 
 auto main（） - > int 
 {
 using namespace std; 
尝试
 {
 for（int precision = 6; precision <= 8; ++ precision）
 {
 test（5.0，precision）; 
} 
 test（0.0，14）; 
返回EXIT_SUCCESS; 
} 
 catch（例外常量& x）
 {
 fprintf（stderr，！％s\，x.what（））; 
} 
 return EXIT_FAILURE; 
 
  

---

适用于Visual C ++ （但Visual C ++似乎缺少相反的转换）：

 
 H：\dev\test\so\0187> < b>  cl / nologo- /？ 2& 1 |找到/ iler ver  
用于x86 
 
的Microsoft（R）C / C ++优化编译器版本18.00.30723 H：\dev\test \so\0187>   cl barx.cpp -D INCLUDE_IOSTREAM / Feb   
 barx.cpp 
 
 H：\dev \test\so\0187>    
十六进制5.000与6位数字：0x1.400000p + 2 
十六进制5.000与7位数字： 0x1.4000000p + 2 
十六进制5.000 8位数字：0x1.40000000p + 2 
十六进制0.000用14位数字：0x0.00000000000000p + 0 
 
 H：\dev\ test\so\0187> _ 
 

---

当<

 
 H：c $ c $< iostream>  \dev\test\so\0187>   g ++ --version |找到++  
 g ++（GCC）4.9.1 
 
 H：\dev\test\so\0187>   g ++ -std = c ++ 11 barx.cpp  
 
 H：\dev\test\so\0187>   a  
十六进制数为5.000，数字为6：0x1.400000p + 2 
十六进制数为5.000，数字为7：0x1.4000000p + 2 
十六进制数为5.000 8位数字：0x1.40000000p + 2 
十六进制为0.000，14位：0x0.00000000000000p + 0 
 
 H：\dev\test\so\0187> _ 
 

---

当时，挂起的奇怪结果包括< iostream> ：

 
 H：\dev\test\so\0187> ;   g ++ -std = c ++ 11 -D INCLUDE_IOSTREAM barx.cpp  
 
 H：\dev\test\so\ 0187> 
十六进制5.000与六位：0xa.000000p-1 
十六进制5.000与七位：0xa.0000000p-1 
十六进制数为5.000,8位：0x0.00000000p-33'奇怪。
 ^ C< i& Hang，Ctrl + C 
 H：\dev\test\so\0187> _ 
 

我正在寻求解决方法或解决方法。

解决方案

微软的实施有许多 printf 错误，并且这些错误会默认影响MinGW（＃377 ，＃407 ，等等）。

在所有情况下，建议似乎是 a>在预处理器中将 __ USE_MINGW_ANSI_STDIO 定义为 1 ，以使用MinGW自己的ANSI兼容实现。

据推测，Visual Studio在底层系统代码中有缺陷的内部解决方法。

Compiler: 64-bit MinGW G++ 4.9.1 from the Nuwen distro, under Windows 8.1.

Code:

#ifdef INCLUDE_IOSTREAM
#   include <iostream>
#endif
#include <stdio.h>      // ::snprintf
#include <stdlib.h>     // EXIT_SUCCESS, EXIT_FAILURE
#include <stdexcept>    // std::exception

#ifdef snprintf
#   error snprintf defined as macro
#endif

#ifdef _MSC_VER
    auto const snprintf = _snprintf;
#endif

void test( double const value, int const precision)
{
    char buffer[34];
    snprintf( buffer, sizeof( buffer ), "%.*a", precision, value );
    printf( "Hex of %.3f with %2d digits: %s\n", value, precision, buffer );
}

auto main() -> int
{
    using namespace std;
    try
    {
        for( int precision = 6; precision <= 8; ++precision )
        {
            test( 5.0, precision );
        }
        test( 0.0, 14 );
        return EXIT_SUCCESS;
    }
    catch( exception const& x )
    {
        fprintf( stderr, "!%s\n", x.what() );
    }
    return EXIT_FAILURE;
}

---

Works fine with Visual C++ (but Visual C++ appears to lack the opposite conversion):

H:\dev\test\so\0187>cl /nologo- /? 2>&1 | find /i "ler ver"
Microsoft (R) C/C++ Optimizing Compiler Version 18.00.30723 for x86

H:\dev\test\so\0187>cl barx.cpp -D INCLUDE_IOSTREAM /Feb
barx.cpp

H:\dev\test\so\0187>b
Hex 5.000 with  6 digits: 0x1.400000p+2
Hex 5.000 with  7 digits: 0x1.4000000p+2
Hex 5.000 with  8 digits: 0x1.40000000p+2
Hex 0.000 with 14 digits: 0x0.00000000000000p+0

H:\dev\test\so\0187>_

---

Also works fine with g++ when <iostream> is not included:

H:\dev\test\so\0187>g++ --version | find "++"
g++ (GCC) 4.9.1

H:\dev\test\so\0187>g++ -std=c++11 barx.cpp

H:\dev\test\so\0187>a
Hex of 5.000 with  6 digits: 0x1.400000p+2
Hex of 5.000 with  7 digits: 0x1.4000000p+2
Hex of 5.000 with  8 digits: 0x1.40000000p+2
Hex of 0.000 with 14 digits: 0x0.00000000000000p+0

H:\dev\test\so\0187>_

---

Bizarre result w/hang when <iostream> is included:

H:\dev\test\so\0187>g++ -std=c++11 -D INCLUDE_IOSTREAM barx.cpp

H:\dev\test\so\0187>a
Hex of 5.000 with  6 digits: 0xa.000000p-1
Hex of 5.000 with  7 digits: 0xa.0000000p-1
Hex of 5.000 with  8 digits: 0x0.00000000p-33           ← Weird.
^C                                                      ← Hang, Ctrl+C
H:\dev\test\so\0187>_

I’m asking for a fix or workaround.

解决方案

Microsoft's implementation has a number of printf bugs, and these affect MinGW by default (#377, #407, et al).

In all cases the recommendation appears to be to define __USE_MINGW_ANSI_STDIO as 1 in the preprocessor to use MinGW's own ANSI-compliant implementation instead.

Presumably, Visual Studio has its own internal workarounds for the flaws in the underlying system code.

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