std :: ostringstream不返回有效的字符串 [英] std::ostringstream isn't returning a valid string

问题描述

我试图使用std :: ostringstream将一个数字转换为字符串（char *），但它似乎并不工作。这里是我有的代码：

  #include< windows.h> 
 #include< sstream> 
 
 int main（）
 {
 std :: ostringstream out; 
 out<< 1234; 
 
 const char * intString = out.str（）。c_str（）; 
 
 MessageBox（NULL，intString，intString，MB_OK | MB_ICONEXCLAMATION）; 
 
 return 0; 
} 
  

生成的消息框中没有文本。

这让我相信，调用 out.str（）。c_str（）字符串，但我不确定。因为我已经裁剪这个程序到目前为止仍然有问题，我必须做一个尴尬的简单的错误。

$ <$>

out.str（）返回一个 std :: string 按值，这意味着你正在调用 .c_str（）一个临时的。因此，在 intString 初始化时，它已经指向无效（已销毁）的数据。

.str（）的结果：

  std： ：string const& str = out.str（）; 
 char const * intString = str.c_str（）; 
  

I'm trying to use std::ostringstream to convert a number into a string (char *), but it doesn't seem to be working. Here's the code I have:

#include <windows.h>
#include <sstream>

int main()
{
    std::ostringstream out;
    out << 1234;

    const char *intString = out.str().c_str();

    MessageBox(NULL, intString, intString, MB_OK|MB_ICONEXCLAMATION);

    return 0;
}

The resulting message box simply has no text in it.

This leads me to believe that the call to out.str().c_str() is returning an invalid string, but I'm not sure. Since I've trimmed this program down so far an am still getting the problem, I must have made an embarrassingly simple mistake. Help is appreciated!

解决方案

out.str() returns a std::string by value, which means that you are calling .c_str() on a temporary. Consequently, by the time intString is initialized, it is already pointing at invalid (destroyed) data.

Cache the result of .str() and work with that:

std::string const& str = out.str();
char const* intString = str.c_str();

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