对有关数据类型转换的整理

int i = 100 ;
2

long l = 2001 ;
3

float f = 300.2 ;
4

double d = 12345.119 ;
5

char username[] = " 程佩君 " ;
6

char temp[ 200 ];
7

char * buf;
8

CString str;
9

_variant_t v1;
10

_bstr_t v2;
11

一、其它数据类型转换为字符串

短整型( int )
2

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
3

itoa(i,temp, 2 ); /**/ ///按二进制方式转换
4

长整型( long )
5

ltoa(l,temp, 10 );
6

浮点数( float , double )
7

用fcvt可以完成转换,这是MSDN中的例子:
8

int decimal , sign;
9

char * buffer;
10

double source = 3.1415926535 ;
11

buffer = _fcvt( source, 7 , & decimal , & sign );
12

运行结果:source: 3.1415926535 buffer: ' 31415927 ' decimal : 1 sign: 0
13

decimal表示小数点的位置,sign表示符号:0为正数，1为负数
14

CString变量
15

str = " 2008北京奥运 " ;
16

buf = (LPSTR)(LPCTSTR)str;
17

BSTR变量
18

BSTR bstrValue = ::SysAllocString(L " 程序员 " );
19

char * buf = _com_util::ConvertBSTRToString(bstrValue);
20

SysFreeString(bstrValue);
21

AfxMessageBox(buf);
22

delete(buf);
23

CComBSTR变量
24

CComBSTR bstrVar( " test " );
25

char * buf = _com_util::ConvertBSTRToString(bstrVar.m_str);
26

AfxMessageBox(buf);
27

delete(buf);
28

_bstr_t变量
30

_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
31

_bstr_t bstrVar( " test " );
32

const char * buf = bstrVar; /**/ ///不要修改buf中的内容
33

AfxMessageBox(buf);
34

通用方法(针对非COM数据类型)
37

用sprintf完成转换
38

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);
40

二、字符串转换为其它数据类型

strcpy(temp, " 123 " );
2

短整型( int )
4

i = atoi(temp);
5

长整型( long )
6

l = atol(temp);
7

浮点( double )
8

d = atof(temp);
9

CString变量
10

CString name = temp;
11

BSTR变量
12

BSTR bstrValue = ::SysAllocString(L " 程序员 " );
13

/**/ ///完成对bstrValue的使用
14

SysFreeString(bstrValue);
15

CComBSTR变量
17

CComBSTR类型变量可以直接赋值
18

CComBSTR bstrVar1( " test " );
19

CComBSTR bstrVar2(temp);
20

_bstr_t变量
22

_bstr_t类型的变量可以直接赋值
23

_bstr_t bstrVar1( " test " );
24

_bstr_t bstrVar2(temp);
25

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:
2

整数( int )
5

str.Format( " %d " ,i);
6

浮点数( float )
7

str.Format( " %f " ,i);
8

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
9

str = username;
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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,但并不直接指向字串的缓冲区。
2

char * 转换到BSTR可以这样:
3

BSTR b = _com_util::ConvertStringToBSTR( " 数据 " ); /**/ ///使用前需要加上comutil.h和comsupp.lib
4

SysFreeString(bstrValue);
5

反之可以使用
6

char * p = _com_util::ConvertBSTRToString(b);
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delete p;
8

具体可以参考一，二段落里的具体说明。
9

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。
11

特别是_bstr_t,建议大家使用它。

五、VARIANT 、_variant_t 与 COleVariant

1 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。
2 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：
3 VARIANT va;
4 int a = 2001 ;
5 va.vt = VT_I4; /**/ ///指明整型数据
6 va.lVal = a; /**/ ///赋值
7
8
9 _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。
10 使用时需加上#include < comdef.h >
11 例如：
12 long l = 222 ;
13 ing i = 100 ;
14 _variant_t lVal(l);
15 lVal = ( long )i;
16
17 COleVariant的使用与_variant_t的方法基本一样，请参考如下例子：
18 COleVariant v3 = " 字符串 " , v4 = ( long ) 1999 ;
19 CString str = (BSTR)v3.pbstrVal;
20 long i = v4.lVal;
21
22 /**/ //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
23 本主题演示如何将各种 C ++ 字符串类型转换为其他字符串。可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。
24
25

        从 char * 转换

1 // 此示例演示如何从 char * 转换为上面列出的其他字符串类型。
2 // convert_from_char.cpp
3 // compile with /clr /link comsuppw.lib
4 #include < iostream >
5 include < stdlib.h > #include < string >
6 #include " atlbase.h " #include " atlstr.h " #include " comutil.h "
7 using namespace std; using namespace System;
8 int main() {    char *orig = "Hello, World!";    cout << orig << " (char *)" << endl;
9    // 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;
10    // Convert to a _bstr_t    _bstr_t bstrt(orig);    bstrt += " (_bstr_t)";    cout << bstrt << endl;
11    // Convert to a CComBSTR    CComBSTR ccombstr(orig);    if (ccombstr.Append(L" (CComBSTR)") == S_OK)    {        CW2A printstr(ccombstr);        cout << printstr << endl;    }
12    // Convert to a CString    CString cstring(orig);    cstring += " (CString)";    cout << cstring << endl;
13    // Convert to a basic_string    string basicstring(orig);    basicstring += " (basic_string)";    cout << basicstring << endl;
14    // Convert to a System::String    String ^systemstring = gcnew String(orig);    systemstring += " (System::String)";    Console::WriteLine("{0}", systemstring);    delete systemstring;}

1 // 输出
2 Hello, World ! ( char * )
3 Hello, World ! (wchar_t * )
4 Hello, World ! (_bstr_t)
5 Hello, World ! (CComBSTR)
6 Hello, World ! (CString)
7 Hello, World ! (basic_string)
8 Hello, World ! (System::String)

       从 wchar_t * 转换

此示例演示如何从 wchar_t * 转换为上面列出的其他字符串类型。
2

// convert_from_wchar_t.cpp // compile with /clr /link comsuppw.lib
4

#include < iostream > #include < stdlib.h > #include < string >
5

#include " atlbase.h " #include " atlstr.h " #include " comutil.h "
6

using namespace std; using namespace System;
7

int main()

{ wchar_t *orig = L"Hello, World!"; wcout << orig << L" (wchar_t *)" << endl;
8

// 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;
9

// Convert to a _bstr_t _bstr_t bstrt(orig); bstrt += " (_bstr_t)"; cout << bstrt << endl;
10

// Convert to a CComBSTR CComBSTR ccombstr(orig); if (ccombstr.Append(L" (CComBSTR)") == S_OK) { CW2A printstr(ccombstr); cout << printstr << endl; }
11

// Convert to a CString CString cstring(orig); cstring += " (CString)"; cout << cstring << endl;
12

// Convert to a basic_string wstring basicstring(orig); basicstring += L" (basic_string)"; wcout << basicstring << endl;
13

// Convert to a System::String String ^systemstring = gcnew String(orig); systemstring += " (System::String)"; Console::WriteLine("{0}", systemstring); delete systemstring;}
14

//输出
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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
2

示例
5

说明
7

此示例演示如何从 _bstr_t 转换为上面列出的其他字符串类型。
8

// convert_from_bstr_t.cpp // compile with /clr /link comsuppw.lib
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#include < iostream > #include < stdlib.h > #include < string >
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#include " atlbase.h " #include " atlstr.h " #include " comutil.h "
12

using namespace std; using namespace System;
13

int main()

{ _bstr_t orig("Hello, World!"); wcout << orig << " (_bstr_t)" << endl;
14

// Convert to a char* const size_t newsize = 100; char nstring[newsize]; strcpy_s(nstring, (char *)orig); strcat_s(nstring, " (char *)"); cout << nstring << endl;
15

// Convert to a wchar_t* wchar_t wcstring[newsize]; wcscpy_s(wcstring, (wchar_t *)orig); wcscat_s(wcstring, L" (wchar_t *)"); wcout << wcstring << endl;
16

// Convert to a CComBSTR CComBSTR ccombstr((char *)orig); if (ccombstr.Append(L" (CComBSTR)") == S_OK) { CW2A printstr(ccombstr); cout << printstr << endl; }
17

// Convert to a CString CString cstring((char *)orig); cstring += " (CString)"; cout << cstring << endl;
18

// Convert to a basic_string string basicstring((char *)orig); basicstring += " (basic_string)"; cout << basicstring << endl;
19

// Convert to a System::String String ^systemstring = gcnew String((char *)orig); systemstring += " (System::String)"; Console::WriteLine("{0}", systemstring); delete systemstring;} 输出
20

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)
21

从 CComBSTR 转换
22

示例
25

说明
27

此示例演示如何从 CComBSTR 转换为上面列出的其他字符串类型。
28

// convert_from_ccombstr.cpp// compile with /clr /link comsuppw.lib
30

#include <iostream>#include <stdlib.h>#include <string>
31

#include "atlbase.h"#include "atlstr.h"#include "comutil.h"#include "vcclr.h"
32

using namespace std;using namespace System;using namespace System::Runtime::InteropServices;
33

int main()

{ CComBSTR orig("Hello, World!"); CW2A printstr(orig); cout << printstr << " (CComBSTR)" << endl;
34

// 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;
35

// Convert to a wchar_t* wchar_t wcstring[newsize]; wcscpy_s(wcstring, orig); wcscat_s(wcstring, L" (wchar_t *)"); wcout << wcstring << endl;
36

// Convert to a _bstr_t_bstr_t bstrt(orig); bstrt += " (_bstr_t)"; cout << bstrt << endl;
37

// Convert to a CString CString cstring(orig); cstring += " (CString)"; cout << cstring << endl;
38

// Convert to a basic_string wstring basicstring(orig); basicstring += L" (basic_string)"; wcout << basicstring << endl;
39

// Convert to a System::String String ^systemstring = gcnew String(orig); systemstring += " (System::String)"; Console::WriteLine("{0}", systemstring); delete systemstring;} 输出
40

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)
41

从 CString 转换
42

示例
45

说明
47

此示例演示如何从 CString 转换为上面列出的其他字符串类型。
48

// convert_from_cstring.cpp// compile with /clr /link comsuppw.lib
50

#include <iostream>#include <stdlib.h>#include <string>
51

#include "atlbase.h"#include "atlstr.h"#include "comutil.h"
52

using namespace std;using namespace System;
53

int main()

{ CString orig("Hello, World!"); wcout << orig << " (CString)" << endl;
54

// Convert to a char* const size_t newsize = 100; char nstring[newsize]; strcpy_s(nstring, orig); strcat_s(nstring, " (char *)"); cout << nstring << endl;
55

// 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;
56

// Convert to a _bstr_t _bstr_t bstrt(orig); bstrt += " (_bstr_t)"; cout << bstrt << endl;
57

// Convert to a CComBSTR CComBSTR ccombstr(orig); if (ccombstr.Append(L" (CComBSTR)") == S_OK) { CW2A printstr(ccombstr); cout << printstr << endl; }
58

// Convert to a basic_string string basicstring(orig); basicstring += " (basic_string)"; cout << basicstring << endl;
59

// Convert to a System::String String ^systemstring = gcnew String(orig); systemstring += " (System::String)"; Console::WriteLine("{0}", systemstring); delete systemstring;} 输出
60

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)
61

从 basic_string 转换
62

示例
65

说明
67

此示例演示如何从 basic_string 转换为上面列出的其他字符串类型。
68

// convert_from_basic_string.cpp// compile with /clr /link comsuppw.lib
70

#include <iostream>#include <stdlib.h>#include <string>
71

#include "atlbase.h"#include "atlstr.h"#include "comutil.h"
72

using namespace std;using namespace System;
73

int main()

{ string orig("Hello, World!"); cout << orig << " (basic_string)" << endl;
74

// 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;
75

// 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;
76

// Convert to a _bstr_t _bstr_t bstrt(orig.c_str()); bstrt += " (_bstr_t)"; cout << bstrt << endl;
77

// Convert to a CComBSTR CComBSTR ccombstr(orig.c_str()); if (ccombstr.Append(L" (CComBSTR)") == S_OK) { CW2A printstr(ccombstr); cout << printstr << endl; }
78

// Convert to a CString CString cstring(orig.c_str()); cstring += " (CString)"; cout << cstring << endl;
79

// Convert to a System::String String ^systemstring = gcnew String(orig.c_str()); systemstring += " (System::String)"; Console::WriteLine("{0}", systemstring); delete systemstring;}输出
80

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)
85

从 System::String 转换
86

示例
89

说明
91

此示例演示如何从 System.String 转换为上面列出的其他字符串类型。
92

// convert_from_system_string.cpp// compile with /clr /link comsuppw.lib
94

#include <iostream>#include <stdlib.h>#include <string>
95

#include "atlbase.h"#include "atlstr.h"#include "comutil.h"#include "vcclr.h"
96

using namespace std;using namespace System;using namespace System::Runtime::InteropServices;
97

int main()

{ String ^orig = gcnew String("Hello, World!"); Console::WriteLine("{0} (System::String)", orig);
98

pin_ptr<const wchar_t> wch = PtrToStringChars(orig);
99

// 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;
100

// Convert to a wchar_t* wchar_t wcstring[newsize]; wcscpy_s(wcstring, wch); wcscat_s(wcstring, L" (wchar_t *)"); wcout << wcstring << endl;
101

// Convert to a _bstr_t _bstr_t bstrt(wch); bstrt += " (_bstr_t)"; cout << bstrt << endl;
102

// Convert to a CComBSTR
103

CComBSTR ccombstr(wch); if (ccombstr.Append(L" (CComBSTR)") == S_OK)

{ CW2A printstr(ccombstr); cout << printstr << endl; }
104

// Convert to a CString CString cstring(wch); cstring += " (CString)"; cout << cstring << endl;
105

// Convert to a basic_string wstring basicstring(wch); basicstring += L" (basic_string)"; wcout << basicstring << endl;
106

delete orig;} 输出
107

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)

对有关数据类型转换的整理

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