如何:在各种字符串类型之间进行转换
本主题演示如何将各种 Visual 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。
示例
说明
此示例演示如何从 char * 转换为上面列出的其他字符串类型。 char * 字符串(也称为 C 样式字符串)使用 null 字符指示字符串的末尾。 C 样式字符串通常每个字符需要一个字节,但也可以使用两个字节。 在下面的示例中,char * 字符串有时称为多字节字符字符串,因为该字符串数据是从 Unicode 字符串转换得到的。 可对 char * 字符串执行单字节和多字节字符 (MBCS) 函数运算。
代码
// 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()
{
// Create and display a C style string, and then use it
// to create different kinds of strings.
char *orig = "Hello, World!";
cout << orig << " (char *)" << endl;
// newsize describes the length of the
// wchar_t string called wcstring in terms of the number
// of wide characters, not the number of bytes.
size_t newsize = strlen(orig) + 1;
// The following creates a buffer large enough to contain
// the exact number of characters in the original string
// in the new format. If you want to add more characters
// to the end of the string, increase the value of newsize
// to increase the size of the buffer.
wchar_t * wcstring = new wchar_t[newsize];
// Convert char* string to a wchar_t* string.
size_t convertedChars = 0;
mbstowcs_s(&convertedChars, wcstring, newsize, orig, _TRUNCATE);
// Display the result and indicate the type of string that it is.
wcout << wcstring << _T(" (wchar_t *)") << endl;
// Convert the C style string to a _bstr_t string.
_bstr_t bstrt(orig);
// Append the type of string to the new string
// and then display the result.
bstrt += " (_bstr_t)";
cout << bstrt << endl;
// Convert the C style string to a CComBSTR string.
CComBSTR ccombstr(orig);
if (ccombstr.Append(_T(" (CComBSTR)")) == S_OK)
{
CW2A printstr(ccombstr);
cout << printstr << endl;
}
// Convert the C style string to a CstringA and display it.
CStringA cstringa(orig);
cstringa += " (CStringA)";
cout << cstringa << endl;
// Convert the C style string to a CStringW and display it.
CStringW cstring(orig);
cstring += " (CStringW)";
// To display a CStringW correctly, use wcout and cast cstring
// to (LPCTSTR).
wcout << (LPCTSTR)cstring << endl;
// Convert the C style string to a basic_string and display it.
string basicstring(orig);
basicstring += " (basic_string)";
cout << basicstring << endl;
// Convert the C style string to a System::String and display it.
String ^systemstring = gcnew String(orig);
systemstring += " (System::String)";
Console::WriteLine("{0}", systemstring);
delete systemstring;
}
Output
Hello, World! (char *)
Hello, World! (wchar_t *)
Hello, World! (_bstr_t)
Hello, World! (CComBSTR)
Hello, World! (CStringA)
Hello, World! (CStringW)
Hello, World! (basic_string)
Hello, World! (System::String)
示例
说明
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。 包括 wchar_t * 在内的一些字符串类型可实现宽字符格式。 若要在多字节和宽字符格式之间转换字符串,则可以使用单个函数调用(如 mbstowcs_s),也可以使用针对类的构造函数调用(如 CStringA)。
代码
// 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()
{
// Create a string of wide characters, display it, and then
// use this string to create other types of strings.
wchar_t *orig = _T("Hello, World!");
wcout << orig << _T(" (wchar_t *)") << endl;
// Convert the wchar_t string to a char* string. Record
//.the length of the original string and add 1 to it to
//.account for the terminating null character.
size_t origsize = wcslen(orig) + 1;
size_t convertedChars = 0;
// Use a multibyte string to append the type of string
// to the new string before displaying the result.
char strConcat[] = " (char *)";
size_t strConcatsize = (strlen( strConcat ) + 1)*2;
// Allocate two bytes in the multibyte output string for every wide
// character in the input string (including a wide character
// null). Because a multibyte character can be one or two bytes,
// you should allot two bytes for each character. Having extra
// space for the new string is not an error, but having
// insufficient space is a potential security problem.
const size_t newsize = origsize*2;
// The new string will contain a converted copy of the original
// string plus the type of string appended to it.
char *nstring = new char[newsize+strConcatsize];
// Put a copy of the converted string into nstring
wcstombs_s(&convertedChars, nstring, newsize, orig, _TRUNCATE);
// append the type of string to the new string.
_mbscat_s((unsigned char*)nstring, newsize+strConcatsize, (unsigned char*)strConcat);
// Display the result.
cout << nstring << endl;
// Convert a wchar_t to a _bstr_t string and display it.
_bstr_t bstrt(orig);
bstrt += " (_bstr_t)";
cout << bstrt << endl;
// Convert the wchar_t string to a BSTR wide character string
// by using the ATL CComBSTR wrapper class for BSTR strings.
// Then display the result.
CComBSTR ccombstr(orig);
if (ccombstr.Append(_T(" (CComBSTR)")) == S_OK)
{
// CW2A converts the string in ccombstr to a multibyte
// string in printstr, used here for display output.
CW2A printstr(ccombstr);
cout << printstr << endl;
// The following line of code is an easier way to
// display wide character strings:
// wcout << (LPCTSTR) ccombstr << endl;
}
// Convert a wide wchar_t string to a multibyte CStringA,
// append the type of string to it, and display the result.
CStringA cstringa(orig);
cstringa += " (CStringA)";
cout << cstringa << endl;
// Convert a wide character wchar_t string to a wide
// character CStringW string and append the type of string to it
CStringW cstring(orig);
cstring += " (CStringW)";
// To display a CStringW correctly, use wcout and cast cstring
// to (LPCTSTR).
wcout << (LPCTSTR)cstring << endl;
// Convert the wide character wchar_t string to a
// basic_string, append the type of string to it, and
// display the result.
wstring basicstring(orig);
basicstring += _T(" (basic_string)");
wcout << basicstring << endl;
// Convert a wide character wchar_t string to a
// System::String string, append the type of string to it,
// and display the result.
String ^systemstring = gcnew String(orig);
systemstring += " (System::String)";
Console::WriteLine("{0}", systemstring);
delete systemstring;
}
Output
Hello, World! (wchar_t *)
Hello, World! (char *)
Hello, World! (_bstr_t)
Hello, World! (CComBSTR)
Hello, World! (CStringA)
Hello, World! (CStringW)
Hello, World! (basic_string)
Hello, World! (System::String)
示例
说明
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。 _bstr_t 对象是一种封装宽字符 BSTR 字符串的方法。 BSTR 字符串具有长度值且不使用 null 字符终止字符串,但所要转换到的目标字符串类型可能需要终止 null。
代码
// 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()
{
// Create a _bstr_t string, display the result, and indicate the
// type of string that it is.
_bstr_t orig("Hello, World!");
wcout << orig << " (_bstr_t)" << endl;
// Convert the wide character _bstr_t string to a C style
// string. To be safe, allocate two bytes for each character
// in the char* string, including the terminating null.
const size_t newsize = (orig.length()+1)*2;
char *nstring = new char[newsize];
// Uses the _bstr_t operator (char *) to obtain a null
// terminated string from the _bstr_t object for
// nstring.
strcpy_s(nstring, newsize, (char *)orig);
strcat_s(nstring, newsize, " (char *)");
cout << nstring << endl;
// Prepare the type of string to append to the result.
wchar_t strConcat[] = _T(" (wchar_t *)");
size_t strConcatLen = wcslen(strConcat) + 1;
// Convert a _bstr_t to a wchar_t* string.
const size_t widesize = orig.length()+ strConcatLen;
wchar_t *wcstring = new wchar_t[newsize];
wcscpy_s(wcstring, widesize, (wchar_t *)orig);
wcscat_s(wcstring, widesize, strConcat);
wcout << wcstring << endl;
// Convert a _bstr_t string to a CComBSTR string.
CComBSTR ccombstr((char *)orig);
if (ccombstr.Append(_T(" (CComBSTR)")) == S_OK)
{
CW2A printstr(ccombstr);
cout << printstr << endl;
}
// Convert a _bstr_t to a CStringA string.
CStringA cstringa(orig.GetBSTR());
cstringa += " (CStringA)";
cout << cstringa << endl;
// Convert a _bstr_t to a CStringW string.
CStringW cstring(orig.GetBSTR());
cstring += " (CStringW)";
// To display a cstring correctly, use wcout and
// "cast" the cstring to (LPCTSTR).
wcout << (LPCTSTR)cstring << endl;
// Convert the _bstr_t to a basic_string.
string basicstring((char *)orig);
basicstring += " (basic_string)";
cout << basicstring << endl;
// Convert the _bstr_t to a System::String.
String ^systemstring = gcnew String((char *)orig);
systemstring += " (System::String)";
Console::WriteLine("{0}", systemstring);
delete systemstring;
}
Output
Hello, World! (_bstr_t)
Hello, World! (char *)
Hello, World! (wchar_t *)
Hello, World! (CComBSTR)
Hello, World! (CStringA)
Hello, World! (CStringW)
Hello, World! (basic_string)
Hello, World! (System::String)
示例
说明
此示例演示如何从 CComBSTR 转换为上面列出的其他字符串类型。 与 _bstr_t 一样,CComBSTR 对象是一种封装宽字符 BSTR 字符串的方法。 BSTR 字符串具有长度值且不使用 null 字符终止字符串,但所要转换到的目标字符串类型可能需要终止 null。
代码
// 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()
{
// Create and initialize a BSTR string by using a CComBSTR object.
CComBSTR orig("Hello, World!");
// Convert the BSTR into a multibyte string, display the result,
// and indicate the type of string that it is.
CW2A printstr(orig);
cout << printstr << " (CComBSTR)" << endl;
// Convert a wide character CComBSTR string to a
// regular multibyte char* string. Allocate enough space
// in the new string for the largest possible result,
// including space for a terminating null.
const size_t newsize = (orig.Length()+1)*2;
char *nstring = new char[newsize];
// Create a string conversion object, copy the result to
// the new char* string, and display the result.
CW2A tmpstr1(orig);
strcpy_s(nstring, newsize, tmpstr1);
cout << nstring << " (char *)" << endl;
// Prepare the type of string to append to the result.
wchar_t strConcat[] = _T(" (wchar_t *)");
size_t strConcatLen = wcslen(strConcat) + 1;
// Convert a wide character CComBSTR string to a wchar_t*.
// The code first determines the length of the converted string
// plus the length of the appended type of string, then
// prepares the final wchar_t string for display.
const size_t widesize = orig.Length()+ strConcatLen;
wchar_t *wcstring = new wchar_t[widesize];
wcscpy_s(wcstring, widesize, orig);
wcscat_s(wcstring, widesize, strConcat);
// Display the result. Unlike CStringW, a wchar_t does not need
// a cast to (LPCTSTR) with wcout.
wcout << wcstring << endl;
// Convert a wide character CComBSTR to a wide character _bstr_t,
// append the type of string to it, and display the result.
_bstr_t bstrt(orig);
bstrt += " (_bstr_t)";
cout << bstrt << endl;
// Convert a wide character CComBSTR to a multibyte CStringA,
// append the type of string to it, and display the result.
CStringA cstringa(orig);
cstringa += " (CStringA)";
cout << cstringa << endl;
// Convert a wide character CComBSTR to a wide character CStringW.
CStringW cstring(orig);
cstring += " (CStringW)";
// To display a cstring correctly, use wcout and cast cstring
// to (LPCTSTR).
wcout << (LPCTSTR)cstring << endl;
// Convert a wide character CComBSTR to a wide character
// basic_string.
wstring basicstring(orig);
basicstring += _T(" (basic_string)");
wcout << basicstring << endl;
// Convert a wide character CComBSTR to a System::String.
String ^systemstring = gcnew String(orig);
systemstring += " (System::String)";
Console::WriteLine("{0}", systemstring);
delete systemstring;
}
Output
Hello, World! (CComBSTR)
Hello, World! (char *)
Hello, World! (wchar_t *)
Hello, World! (_bstr_t)
Hello, World! (CStringA)
Hello, World! (CStringW)
Hello, World! (basic_string)
Hello, World! (System::String)
示例
说明
此示例演示如何从 CString 转换为上面列出的其他字符串类型。 CString 基于 TCHAR 数据类型,而后者又依赖于是否定义了 _UNICODE 符号。 如果未定义 _UNICODE,则 TCHAR 定义为 char 且 CString 包含一个多字节字符字符串;如果定义了 _UNICODE,则 TCHAR 定义为 wchar_t 且 CString 包含一个宽字符字符串。
CStringA 是 CString 的多字节字符串的始终版本;CStringW 是宽字符字符串的唯一版本。 CStringA 和 CStringW 都不使用 _UNICODE 确定它们应采用的编译方式。 此示例使用 CStringA 和 CStringW 明确指定缓冲区大小分配和输出处理中的一些细微差异。
代码
// 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()
{
// Set up a multibyte CStringA string.
CStringA origa("Hello, World!");
cout << origa << " (CStringA)" << endl;
// Set up a wide character CStringW string.
CStringW origw("Hello, World!");
wcout << (LPCTSTR)origw << _T(" (CStringW)") << endl;
// Convert to a char* string from CStringA string
// and display the result.
const size_t newsizea = (origa.GetLength() + 1);
char *nstringa = new char[newsizea];
strcpy_s(nstringa, newsizea, origa);
cout << nstringa << " (char *)" << endl;
// Convert to a char* string from a wide character
// CStringW string. To be safe, we allocate two bytes for each
// character in the original string, including the terminating
// null.
const size_t newsizew = (origw.GetLength() + 1)*2;
char *nstringw = new char[newsizew];
size_t convertedCharsw = 0;
wcstombs_s(&convertedCharsw, nstringw, newsizew, origw, _TRUNCATE );
cout << nstringw << " (char *)" << endl;
// Convert to a wchar_t* from CStringA
size_t convertedCharsa = 0;
wchar_t *wcstring = new wchar_t[newsizea];
mbstowcs_s(&convertedCharsa, wcstring, newsizea, origa, _TRUNCATE);
wcout << wcstring << _T(" (wchar_t *)") << endl;
// Convert to a wide character wchar_t* string from
// a wide character CStringW string.
wchar_t *n2stringw = new wchar_t[newsizew];
wcscpy_s( n2stringw, newsizew, origw );
wcout << n2stringw << _T(" (wchar_t *)") << endl;
// Convert to a wide character _bstr_t string from
// a multibyte CStringA string.
_bstr_t bstrt(origa);
bstrt += _T(" (_bstr_t)");
wcout << bstrt << endl;
// Convert to a wide character_bstr_t string from
// a wide character CStringW string.
bstr_t bstrtw(origw);
bstrtw += " (_bstr_t)";
wcout << bstrtw << endl;
// Convert to a wide character CComBSTR string from
// a multibyte character CStringA string.
CComBSTR ccombstr(origa);
if (ccombstr.Append(_T(" (CComBSTR)")) == S_OK)
{
// Convert the wide character string to multibyte
// for printing.
CW2A printstr(ccombstr);
cout << printstr << endl;
}
// Convert to a wide character CComBSTR string from
// a wide character CStringW string.
CComBSTR ccombstrw(origw);
// Append the type of string to it, and display the result.
if (ccombstrw.Append(_T(" (CComBSTR)")) == S_OK)
{
CW2A printstrw(ccombstrw);
wcout << printstrw << endl;
}
// Convert a multibyte character CStringA to a
// multibyte version of a basic_string string.
string basicstring(origa);
basicstring += " (basic_string)";
cout << basicstring << endl;
// Convert a wide character CStringW to a
// wide character version of a basic_string
// string.
wstring basicstringw(origw);
basicstringw += _T(" (basic_string)");
wcout << basicstringw << endl;
// Convert a multibyte character CStringA to a
// System::String.
String ^systemstring = gcnew String(origa);
systemstring += " (System::String)";
Console::WriteLine("{0}", systemstring);
delete systemstring;
// Convert a wide character CStringW to a
// System::String.
String ^systemstringw = gcnew String(origw);
systemstringw += " (System::String)";
Console::WriteLine("{0}", systemstringw);
delete systemstringw;
}
Output
Hello, World! (CStringA)
Hello, World! (CStringW)
Hello, World! (char *)
Hello, World! (char *)
Hello, World! (wchar_t *)
Hello, World! (wchar_t *)
Hello, World! (_bstr_t)
Hello, World! (_bstr_t)
Hello, World! (CComBSTR)
Hello, World! (CComBSTR)
Hello, World! (basic_string)
Hello, World! (System::String)
示例
说明
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。
代码
// convert_from_basic_string.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()
{
// Set up a basic_string string.
string orig("Hello, World!");
cout << orig << " (basic_string)" << endl;
// Convert a wide char basic_string string to a multibyte char*
// string. To be safe, we allocate two bytes for each character
// in the original string, including the terminating null.
const size_t newsize = (strlen(orig.c_str()) + 1)*2;
char *nstring = new char[newsize];
strcpy_s(nstring, newsize, orig.c_str());
cout << nstring << " (char *)" << endl;
// Convert a basic_string string to a wide character
// wchar_t* string. You must first convert to a char*
// for this to work.
const size_t newsizew = strlen(orig.c_str()) + 1;
size_t convertedChars = 0;
wchar_t *wcstring = new wchar_t[newsizew];
mbstowcs_s(&convertedChars, wcstring, newsizew, orig.c_str(), _TRUNCATE);
wcout << wcstring << _T(" (wchar_t *)") << endl;
// Convert a basic_string string to a wide character
// _bstr_t string.
_bstr_t bstrt(orig.c_str());
bstrt += _T(" (_bstr_t)");
wcout << bstrt << endl;
// Convert a basic_string string to a wide character
// CComBSTR string.
CComBSTR ccombstr(orig.c_str());
if (ccombstr.Append(_T(" (CComBSTR)")) == S_OK)
{
// Make a multibyte version of the CComBSTR string
// and display the result.
CW2A printstr(ccombstr);
cout << printstr << endl;
}
// Convert a basic_string string into a multibyte
// CStringA string.
CStringA cstring(orig.c_str());
cstring += " (CStringA)";
cout << cstring << endl;
// Convert a basic_string string into a wide
// character CStringW string.
CStringW cstringw(orig.c_str());
cstringw += _T(" (CStringW)");
wcout << (LPCTSTR)cstringw << endl;
// Convert a basic_string string to a System::String
String ^systemstring = gcnew String(orig.c_str());
systemstring += " (System::String)";
Console::WriteLine("{0}", systemstring);
delete systemstring;
}
Output
Hello, World! (basic_string)
Hello, World! (char *)
Hello, World! (wchar_t *)
Hello, World! (_bstr_t)
Hello, World! (CComBSTR)
Hello, World! (CStringA)
Hello, World! (CStringW)
Hello, World! (System::String)
示例
说明
此示例演示如何从宽字符 (Unicode) [System::String] 转换为上面列出的其他字符串类型。
代码
// 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()
{
// Set up a System::String and display the result.
String ^orig = gcnew String("Hello, World!");
Console::WriteLine("{0} (System::String)", orig);
// Obtain a pointer to the System::String in order to
// first lock memory into place, so that the
// Garbage Collector (GC) cannot move that object
// while we call native functions.
pin_ptr<const wchar_t> wch = PtrToStringChars(orig);
// Make a copy of the system string as a multibyte
// char* string. Allocate two bytes in the multibyte
// output string for every wide character in the input
// string, including space for a terminating null.
size_t origsize = wcslen(wch) + 1;
const size_t newsize = origsize*2;
size_t convertedChars = 0;
char *nstring = new char[newsize];
wcstombs_s(&convertedChars, nstring, newsize, wch, _TRUNCATE);
cout << nstring << " (char *)" << endl;
// Convert a wide character system string to a
// wide character wchar_t* string.
const size_t newsizew = origsize;
wchar_t *wcstring = new wchar_t[newsizew];
wcscpy_s(wcstring, newsizew, wch);
wcout << wcstring << _T(" (wchar_t *)") << endl;
// Convert a wide character system string to a
// wide character _bstr_t string.
_bstr_t bstrt(wch);
bstrt += " (_bstr_t)";
cout << bstrt << endl;
// Convert a wide character system string
// to a wide character CComBSTR string.
CComBSTR ccombstr(wch);
if (ccombstr.Append(_T(" (CComBSTR)")) == S_OK)
{
// Make a multibyte copy of the CComBSTR string
// and display the result.
CW2A printstr(ccombstr);
cout << printstr << endl;
}
// Convert a wide character System::String to
// a multibyte CStringA string.
CStringA cstring(wch);
cstring += " (CStringA)";
cout << cstring << endl;
// Convert a wide character System::String to
// a wide character CStringW string.
CStringW cstringw(wch);
cstringw += " (CStringW)";
wcout << (LPCTSTR)cstringw << endl;
// Convert a wide character System::String to
// a wide character basic_string.
wstring basicstring(wch);
basicstring += _T(" (basic_string)");
wcout << basicstring << endl;
delete orig;
}
Output
Hello, World! (System::String)
Hello, World! (char *)
Hello, World! (wchar_t *)
Hello, World! (_bstr_t)
Hello, World! (CComBSTR)
Hello, World! (CStringA)
Hello, World! (CStringW)
Hello, World! (basic_string)
请参见
任务
如何:将 System::String 转换为 wchar_t* 或 char*