如何将CString传递到格式字符串％s？ [英] How can CString be passed to format string %s?

问题描述

class MyString
{
public:
    MyString(const std::wstring& s2)
    {
        s = s2;
    }

    operator LPCWSTR() const
    {
        return s.c_str();
    }
private:
    std::wstring s;
};

int _tmain(int argc, _TCHAR* argv[])
{
    MyString s = L"MyString";
    CStringW cstring = L"CString";
    wprintf(L"%s\n", (LPCWSTR)cstring); // Okay. Becase it has an operator LPCWSTR()
    wprintf(L"%s\n", cstring); // Okay, fine. But how?        
    wprintf(L"%s\n", (LPCWSTR)s); // Okay. fine.
    wprintf(L"%s\n", s); // Doesn't work. Why? It prints gabage string like "?."
    return 0;
}

CString如何传递到格式字符串％s？

How can CString be passed to format string %s?

顺便说一句， MSDN说< a>（很奇怪）

By the way, MSDN says(it's weird)

在变量参数函数中使用CString对象

将CString显式转换为一个LPCTSTR字符串，如下所示：

To use a CString object in a variable argument function
Explicitly cast the CString to an LPCTSTR string, as shown here:

CString kindOfFruit = "bananas";
int      howmany = 25;
printf( "You have %d %s\n", howmany, (LPCTSTR)kindOfFruit ); 

推荐答案

CString是专门设计的，指向缓冲区类中的字符串数据。它通过值传递给printf，然后在格式字符串中看到％s时将其视为一个指针。

CString is specifically designed such that it only contains a pointer that points to the string data in a buffer class. It is passed by value to printf which then treats it as a pointer when seeing the "%s" in the format string.

它最初只是使用printf机会，但这后来一直保持作为类接口的一部分。

It originally just happened to work with printf by chance, but this has later been kept as part of the class interface.

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