字符串转换 - 应该熟练掌握的东西

于 2009-01-12 00:35:49 发布
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分类专栏： c 文章标签： C C++ C# 数据结构 F#
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本文链接：https://blog.youkuaiyun.com/iteye_19488/article/details/81677788
本文详细介绍了C++中各种数据类型之间的转换方法，包括基本数据类型转换为字符串、字符串转换为其他数据类型、以及不同类型字符串间的相互转换。通过具体的示例代码展示了如何实现这些转换。

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一、其它数据类型转换为字符串

  • 短整型(int)
    itoa(i,temp,10);///将i转换为字符串放入temp中,最后一个数字表示十进制
    itoa(i,temp,2); ///按二进制方式转换
  • 长整型(long)
    ltoa(l,temp,10);
  • 浮点数(float,double)
    用fcvt可以完成转换,这是MSDN中的例子:
    int decimal, sign;
    char *buffer;
    double source = 3.1415926535;
    buffer = _fcvt( source, 7, &decimal, &sign );
    运行结果:source: 3.1415926535 buffer: '31415927' decimal: 1 sign: 0
    decimal表示小数点的位置,sign表示符号:0为正数，1为负数
  • CString变量
    str = "2008北京奥运";
    buf = (LPSTR)(LPCTSTR)str;
  • BSTR变量
    BSTR bstrValue = ::SysAllocString(L"程序员");
    char * buf = _com_util::ConvertBSTRToString(bstrValue);
    SysFreeString(bstrValue);
    AfxMessageBox(buf);
    delete(buf);
  • CComBSTR变量
    CComBSTR bstrVar("test");
    char *buf = _com_util::ConvertBSTRToString(bstrVar.m_str);
    AfxMessageBox(buf);
    delete(buf);
  • _bstr_t变量
    _bstr_t类型是对BSTR的封装，因为已经重载了=操作符，所以很容易使用
    _bstr_t bstrVar("test");
    const char *buf = bstrVar;///不要修改buf中的内容
    AfxMessageBox(buf);
  • 通用方法(针对非COM数据类型)
    用sprintf完成转换
    char buffer[200]; char c = '1'; int i = 35; long j = 1000; float f = 1.7320534f; sprintf( buffer, "%c",c); sprintf( buffer, "%d",i); sprintf( buffer, "%d",j); sprintf( buffer, "%f",f);    二、字符串转换为其它数据类型
    strcpy(temp,"123");
  • 短整型(int)
            i = atoi(temp);
  • 长整型(long)    l = atol(temp);
  • 浮点(double)          d = atof(temp);

 

  •    
  • CString变量    CString name = temp;
  • BSTR变量    BSTR bstrValue = ::SysAllocString(L"程序员");


           ...///完成对bstrValue的使用           SysFreeString(bstrValue);

  •    
  • CComBSTR变量    CComBSTR类型变量可以直接赋值    CComBSTR bstrVar1("test");    CComBSTR bstrVar2(temp);
  • _bstr_t变量    _bstr_t类型的变量可以直接赋值    _bstr_t bstrVar1("test");
        _bstr_t bstrVar2(temp);

三、其它数据类型转换到CString使用CString的成员函数Format来转换,例如:

  •    
  • 整数(int)    str.Format("%d",i);
  • 浮点数(float)    str.Format("%f",i);
  • 字符串指针(char *)等已经被CString构造函数支持的数据类型可以直接赋值    str = username;
  • 对于Format所不支持的数据类型，可以通过上面所说的关于其它数据类型转化到char *的方法先转到char *，然后赋值给CString变量。

四、BSTR、_bstr_t与CComBSTR

  •    
  • CComBSTR 是ATL对BSTR的封装，_bstr_t是C++对BSTR的封装,BSTR是32位指针,但并不直直指向字串的缓冲区。    char *转换到BSTR可以这样:    BSTR b=_com_util::ConvertStringToBSTR("数据");///使用前需要加上comutil.h和comsupp.lib    SysFreeString(bstrValue);    反之可以使用    char *p=_com_util::ConvertBSTRToString(b);    delete p;    具体可以参考一，二段落里的具体说明。
        CComBSTR与_bstr_t对大量的操作符进行了重载，可以直接进行=,!=,==等操作，所以使用非常方便。
        特别是_bstr_t,建议大家使用它。

五、VARIANT 、_variant_t 与 COleVariant
VARIANT的结构可以参考头文件VC98\Include\OAIDL.H中关于结构体tagVARIANT的定义。
对于VARIANT变量的赋值：首先给vt成员赋值，指明数据类型，再对联合结构中相同数据类型的变量赋值，举个例子：
VARIANT va;
int a=2001;
va.vt=VT_I4;///指明整型数据
va.lVal=a; ///赋值
_variant_t是VARIANT的封装类，其赋值可以使用强制类型转换，其构造函数会自动处理这些数据类型。
使用时需加上#include <comdef.h>
例如：
long l=222;
ing i=100;
_variant_t lVal(l);
lVal = (long)i;

COleVariant的使用与_variant_t的方法基本一样，请参考如下例子：
COleVariant v3 = "字符串", v4 = (long)1999;
CString str =(BSTR)v3.pbstrVal;
long i = v4.lVal;

////////////////////////////////////////////////////////////////////////////////////
本主题演示如何将各种 C++ 字符串类型转换为其他字符串。以转换的字符串类型包括 char *、wchar_t*、_bstr_t、CComBSTR、CString、basic_string 和 System.String。在所有情况下，在将字符串转换为新类型时，都会创建字符串的副本。对新字符串进行的任何更改都不会影响原始字符串，反之亦然。

从 char * 转换

// convert_from_char.cpp
// compile with /clr /link comsuppw.lib

#include <iostream>
#include <stdlib.h>
#include <string>

#include "atlbase.h"
#include "atlstr.h"
#include "comutil.h"

using namespace std;
using namespace System;

int main()
{
     char *orig = "Hello, World!";
     cout << orig << " (char *)" << endl;

     // Convert to a wchar_t*
     size_t origsize = strlen(orig) + 1;
     const size_t newsize = 100;
     size_t convertedChars = 0;
     wchar_t wcstring[newsize];
     mbstowcs_s(&convertedChars, wcstring, origsize, orig, _TRUNCATE);
     wcscat_s(wcstring, L" (wchar_t *)");
     wcout << wcstring << endl;

     // Convert to a _bstr_t
     _bstr_t bstrt(orig);
     bstrt += " (_bstr_t)";
     cout << bstrt << endl;

     // Convert to a CComBSTR
     CComBSTR ccombstr(orig);
     if (ccombstr.Append(L" (CComBSTR)") == S_OK)
     {
         CW2A printstr(ccombstr);
         cout << printstr << endl;
     }

     // Convert to a CString
     CString cstring(orig);
     cstring += " (CString)";
     cout << cstring << endl;

     // Convert to a basic_string
     string basicstring(orig);
     basicstring += " (basic_string)";
     cout << basicstring << endl;

     // Convert to a System::String
     String ^systemstring = gcnew String(orig);
     systemstring += " (System::String)";
     Console::WriteLine("{0}", systemstring);
     delete systemstring;
}

输出
Hello, World! (char *)
Hello, World! (wchar_t *)
Hello, World! (_bstr_t)
Hello, World! (CComBSTR)
Hello, World! (CString)
Hello, World! (basic_string)
Hello, World! (System::String)

从 wchar_t * 转换  
// convert_from_wchar_t.cpp
// compile with /clr /link comsuppw.lib

#include <iostream>
#include <stdlib.h>
#include <string>

#include "atlbase.h"
#include "atlstr.h"
#include "comutil.h"

using namespace std;
using namespace System;

int main()
{
     wchar_t *orig = L"Hello, World!";
     wcout << orig << L" (wchar_t *)" << endl;

     // Convert to a char*
     size_t origsize = wcslen(orig) + 1;
     const size_t newsize = 100;
     size_t convertedChars = 0;
     char nstring[newsize];
     wcstombs_s(&convertedChars, nstring, origsize, orig, _TRUNCATE);
     strcat_s(nstring, " (char *)");
     cout << nstring << endl;

     // Convert to a _bstr_t
     _bstr_t bstrt(orig);
     bstrt += " (_bstr_t)";
     cout << bstrt << endl;

     // Convert to a CComBSTR
     CComBSTR ccombstr(orig);
     if (ccombstr.Append(L" (CComBSTR)") == S_OK)
     {
         CW2A printstr(ccombstr);
         cout << printstr << endl;
     }

     // Convert to a CString
     CString cstring(orig);
     cstring += " (CString)";
     cout << cstring << endl;

     // Convert to a basic_string
     wstring basicstring(orig);
     basicstring += L" (basic_string)";
     wcout << basicstring << endl;

     // Convert to a System::String
     String ^systemstring = gcnew String(orig);
     systemstring += " (System::String)";
     Console::WriteLine("{0}", systemstring);
     delete systemstring;
}

输出
Hello, World! (wchar_t *)
Hello, World! (char *)
Hello, World! (_bstr_t)
Hello, World! (CComBSTR)
Hello, World! (CString)
Hello, World! (basic_string)
Hello, World! (System::String)

  • 从 _bstr_t 转换// convert_from_bstr_t.cpp
    // compile with /clr /link comsuppw.lib

    #include <iostream>
    #include <stdlib.h>
    #include <string>

    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"

    using namespace std;
    using namespace System;

    int main()
    {
         _bstr_t orig("Hello, World!");
         wcout << orig << " (_bstr_t)" << endl;         // Convert to a char*
         const size_t newsize = 100;
         char nstring[newsize];
         strcpy_s(nstring, (char *)orig);
         strcat_s(nstring, " (char *)");
         cout << nstring << endl;         // Convert to a wchar_t*
         wchar_t wcstring[newsize];
         wcscpy_s(wcstring, (wchar_t *)orig);
         wcscat_s(wcstring, L" (wchar_t *)");
         wcout << wcstring << endl;         // Convert to a CComBSTR
         CComBSTR ccombstr((char *)orig);
         if (ccombstr.Append(L" (CComBSTR)") == S_OK)
         {
             CW2A printstr(ccombstr);
             cout << printstr << endl;
         }         // Convert to a CString
         CString cstring((char *)orig);
         cstring += " (CString)";
         cout << cstring << endl;         // Convert to a basic_string
         string basicstring((char *)orig);
         basicstring += " (basic_string)";
         cout << basicstring << endl;         // Convert to a System::String
         String ^systemstring = gcnew String((char *)orig);
         systemstring += " (System::String)";
         Console::WriteLine("{0}", systemstring);
         delete systemstring;
    }
    输出

    Hello, World! (_bstr_t)Hello, World! (char *)Hello, World! (wchar_t *)Hello, World! (CComBSTR)Hello, World! (CString)Hello, World! (basic_string)Hello, World! (System::String)

  • 从 CComBSTR 转换
    // convert_from_ccombstr.cpp
    // compile with /clr /link comsuppw.lib

    #include <iostream>
    #include <stdlib.h>
    #include <string>

    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    #include "vcclr.h"

    using namespace std;
    using namespace System;
    using namespace System::Runtime::InteropServices;

    int main()
    {
        CComBSTR orig("Hello, World!");
        CW2A printstr(orig);
        cout << printstr << " (CComBSTR)" << endl;

        // Convert to a char*
        const size_t newsize = 100;
        char nstring[newsize];
        CW2A tmpstr1(orig);
        strcpy_s(nstring, tmpstr1);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;

        // Convert to a wchar_t*
        wchar_t wcstring[newsize];
        wcscpy_s(wcstring, orig);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;

        // Convert to a _bstr_t
        _bstr_t bstrt(orig);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;

        // Convert to a CString
        CString cstring(orig);
        cstring += " (CString)";
        cout << cstring << endl;

        // Convert to a basic_string
        wstring basicstring(orig);
        basicstring += L" (basic_string)";
        wcout << basicstring << endl;

        // Convert to a System::String
        String ^systemstring = gcnew String(orig);
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }

    输出Hello, World! (CComBSTR)Hello, World! (char *)Hello, World! (wchar_t *)Hello, World! (_bstr_t)Hello, World! (CString)Hello, World! (basic_string)Hello, World! (System::String)

    从 CString 转换
    // convert_from_cstring.cpp
    // compile with /clr /link comsuppw.lib

    #include <iostream>
    #include <stdlib.h>
    #include <string>

    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"

    using namespace std;
    using namespace System;

    int main()
    {
        CString orig("Hello, World!");
        wcout << orig << " (CString)" << endl;

        // Convert to a char*
        const size_t newsize = 100;
        char nstring[newsize];
        strcpy_s(nstring, orig);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;

        // Convert to a wchar_t*
        // You must first convert to a char * for this to work.
        size_t origsize = strlen(orig) + 1;
        size_t convertedChars = 0;
        wchar_t wcstring[newsize];
        mbstowcs_s(&convertedChars, wcstring, origsize, orig, _TRUNCATE);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;

        // Convert to a _bstr_t
        _bstr_t bstrt(orig);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;

        // Convert to a CComBSTR
        CComBSTR ccombstr(orig);
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }

        // Convert to a basic_string
        string basicstring(orig);
        basicstring += " (basic_string)";
        cout << basicstring << endl;

        // Convert to a System::String
        String ^systemstring = gcnew String(orig);
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }
    输出
    Hello, World! (CString)
    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (_bstr_t)
    Hello, World! (CComBSTR)
    Hello, World! (basic_string)
    Hello, World! (System::String)
         从basic_string 转换
    #include <iostream>
    #include <stdlib.h>
    #include <string>

    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"

    using namespace std;
    using namespace System;

    int main()
    {
        string orig("Hello, World!");
        cout << orig << " (basic_string)" << endl;

        // Convert to a char*
        const size_t newsize = 100;
        char nstring[newsize];
        strcpy_s(nstring, orig.c_str());
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;

        // Convert to a wchar_t*
        // You must first convert to a char * for this to work.
        size_t origsize = strlen(orig.c_str()) + 1;
        size_t convertedChars = 0;
        wchar_t wcstring[newsize];
        mbstowcs_s(&convertedChars, wcstring, origsize, orig.c_str(), _TRUNCATE);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;

        // Convert to a _bstr_t
        _bstr_t bstrt(orig.c_str());
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;

        // Convert to a CComBSTR
        CComBSTR ccombstr(orig.c_str());
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }

        // Convert to a CString
        CString cstring(orig.c_str());
        cstring += " (CString)";
        cout << cstring << endl;

        // Convert to a System::String
        String ^systemstring = gcnew String(orig.c_str());
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }
    输出
    Hello, World! (basic_string)
    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (_bstr_t)
    Hello, World! (CComBSTR)
    Hello, World! (CString)
    Hello, World! (System::String)
       
    从 System::String 转换// convert_from_system_string.cpp
    // compile with /clr /link comsuppw.lib

    #include <iostream>
    #include <stdlib.h>
    #include <string>

    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    #include "vcclr.h"

    using namespace std;
    using namespace System;
    using namespace System::Runtime::InteropServices;

    int main()
    {
        String ^orig = gcnew String("Hello, World!");
        Console::WriteLine("{0} (System::String)", orig);

        pin_ptr<const wchar_t> wch = PtrToStringChars(orig);

        // Convert to a char*
        size_t origsize = wcslen(wch) + 1;
        const size_t newsize = 100;
        size_t convertedChars = 0;
        char nstring[newsize];
        wcstombs_s(&convertedChars, nstring, origsize, wch, _TRUNCATE);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;

        // Convert to a wchar_t*
        wchar_t wcstring[newsize];
        wcscpy_s(wcstring, wch);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;

        // Convert to a _bstr_t
        _bstr_t bstrt(wch);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;

        // Convert to a CComBSTR
        CComBSTR ccombstr(wch);
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }

        // Convert to a CString
        CString cstring(wch);
        cstring += " (CString)";
        cout << cstring << endl;

        // Convert to a basic_string
        wstring basicstring(wch);
        basicstring += L" (basic_string)";
        wcout << basicstring << endl;

        delete orig;
    }
    输出Hello, World! (System::String)Hello, World! (char *)Hello, World! (wchar_t *)Hello, World! (_bstr_t)Hello, World! (CComBSTR)Hello, World! (CString)Hello, World! (basic_string)源www.cnblogs.com/zhucl1006/archive/2008/01/04/1025959.html
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