轉型運算子：)

發行項
02/28/2013

型別轉換會提供一種方法中的特定狀況的物件型別的明確轉換。

unary-expression
( type-name ) cast-expression

備註

所有一元 (unary) 運算式被視為 cast 運算式。

編譯器會將轉型運算式 為型別 型別名稱在進行型別轉換之後。轉換 (cast) 可用於任何純量型別的物件或將轉換為從任何其他純量型別。明確型別轉換 (cast) 都會受到相同規則，判斷的隱含轉換效果。在 [轉換 (cast) 上的其他限制可能會產生實際的大小或特定類型的表示。

範例

// expre_CastOperator.cpp
// compile with: /EHsc
// Demonstrate cast operator
#include <iostream>

using namespace std;

int main()
{
    double x = 3.1;
    int i;
    cout << "x = " << x << endl;
    i = (int)x;   // assign i the integer part of x
    cout << "i = " << i << endl;
}

// expre_CastOperator2.cpp
// The following sample shows how to define and use a cast operator. 
#include <string.h>
#include <stdio.h>

class CountedAnsiString
{
public:
    // Assume source is not null terminated
    CountedAnsiString(const char *pStr, size_t nSize) :
                      m_nSize(nSize)
    {
        m_pStr = new char[sizeOfBuffer];

        strncpy_s(m_pStr, sizeOfBuffer, pStr, m_nSize);
        memset(&m_pStr[m_nSize], '!', 9); // for demonstration purposes.
    }

    // Various string-like methods...

    const char *GetRawBytes() const
    {
        return(m_pStr);
    }

    // 
    // operator to cast to a const char *
    // 
    operator const char *()
    {
        m_pStr[m_nSize] = '\0';
        return(m_pStr);
    }

    enum
    {
        sizeOfBuffer = 20
    } size;

private:
    char *m_pStr;
    const size_t m_nSize;
};

int main()
{
    const char *kStr = "Excitinggg";
    CountedAnsiString myStr(kStr, 8);

    const char *pRaw = myStr.GetRawBytes();
    printf_s("RawBytes truncated to 10 chars:   %.10s\n", pRaw);

    const char *pCast = myStr; // or (const char *)myStr;
    printf_s("Casted Bytes:   %s\n", pCast);

    puts("Note that the cast changed the raw internal string");
    printf_s("Raw Bytes after cast:   %s\n", pRaw);
}