C有关数据类型转换大全

1、C+有关数据类型转换大全 来源：中国自学编程网 发布日期：2007-05-21 int i = 100; long l = 2001; float f=300.2; double d=12345.119; char username="程佩君" char temp200; char *buf; CString str; _variant_t v1; _bstr_t v2; 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(lon

2、g) 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 = "20

3、08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:ConvertBSTRToStrin

4、g(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 buffer200; char c = 1; int i = 35; long j = 1000; float f = 1.7320534f;

5、 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; B

6、STR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 Page_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CS

7、tring 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+

8、对BSTR的封装,BSTR是32位指针,但并不直接指向字串的缓冲区。 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_

9、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VC98IncludeOAIDL.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 <co

10、mdef.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。可以转换的字符串类型包括 char *、wchar_t*、_bstr_t、CComBSTR、CString

11、、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 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。 / convert_from_char.cpp / compile with /clr /link comsuppw.lib #include <iostream> #include <stdlib.h> Page#include <string> #include "a

12、tlbase.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; cons

13、t size_t newsize = 100; size_t convertedChars = 0; wchar_t wcstringnewsize; 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

14、)" 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 <&l

15、t; 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(&q

16、uot;0", systemstring); Page 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 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。 / con

17、vert_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 =

18、 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 nstringnewsize; wcstombs_s(&convertedChars, nstring, origsize, orig, _TRUNCATE);

19、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 pr

20、intstr(ccombstr); cout << printstr << endl; / Convert to a CString CString cstring(orig); cstring += " (CString)" cout << cstring << endl; Page / Convert to a basic_string wstring basicstring(orig); basicstring += L" (basic_string)" wcout << basicstr

21、ing << 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! (CComB

22、STR) Hello, World! (CString) Hello, World! (basic_string) Hello, World! (System:String) 从 _bstr_t 转换 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。 / convert_from_bstr_t.cpp / compile with /clr /link comsuppw.lib #include <iostream> #include <stdlib.h> #include <string> #include "atl

23、base.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 nstringn

24、ewsize; strcpy_s(nstring, (char *)orig); strcat_s(nstring, " (char *)"); cout << nstring << endl; / Convert to a wchar_t* wchar_t wcstringnewsize; wcscpy_s(wcstring, (wchar_t *)orig); wcscat_s(wcstring, L" (wchar_t *)"); wcout << wcstring << endl; / Conver

25、t to a CComBSTR CComBSTR ccombstr(char *)orig); if (ccombstr.Append(L" (CComBSTR)") = S_OK) Page CW2A printstr(ccombstr); cout << printstr << endl; / Convert to a CString CString cstring(char *)orig); cstring += " (CString)" cout << cstring << endl; / Conv

26、ert 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", syste

27、mstring); 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 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。 / convert_from_ccombstr.cpp /

28、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 Syste

29、m: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 nstringnewsize; CW2A tmpstr1(orig); strcpy_s(nstring, tmpstr1); Page strca

30、t_s(nstring, " (char *)"); cout << nstring << endl; / Convert to a wchar_t* wchar_t wcstringnewsize; wcscpy_s(wcstring, orig); wcscat_s(wcstring, L" (wchar_t *)"); wcout << wcstring << endl; / Convert to a _bstr_t _bstr_t bstrt(orig); bstrt += " (_bst

31、r_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 << en

32、dl; / 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, Wor

33、ld! (CString) Hello, World! (basic_string) Hello, World! (System:String) 从 CString 转换 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。 / convert_from_cstring.cpp / compile with /clr /link comsuppw.lib #include <iostream> #include <stdlib.h> #include <string> #include "atlbase.h" #

34、include "atlstr.h" #include "comutil.h" using namespace std; using namespace System; int main() CString orig("Hello, World!"); wcout << orig << " (CString)" << endl; Page / Convert to a char* const size_t newsize = 100; char nstringnewsize; s

35、trcpy_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 wcstringnewsize; mbstowcs_s(&convertedChars

36、, 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.A

37、ppend(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 St

38、ring(orig); systemstring += " (System:String)" Console:WriteLine("0", systemstring); delete systemstring; 输出 Hello, World! (CString) Hello, World! (char *) PageHello, World! (wchar_t *) Hello, World! (_bstr_t) Hello, World! (CComBSTR) Hello, World! (basic_string) Hello, World! (S

39、ystem:String) 从 basic_string 转换 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。 / 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 "

40、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 nstringnewsize; strcpy_s(nstring, orig.c_str(); strcat_s(nstrin

41、g, " (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 wcstringnewsize; mbstowcs_s(&convertedChars, wcstring, origsize, orig.c_str

42、(), _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&qu

43、ot; (CComBSTR)") = S_OK) CW2A printstr(ccombstr); Page 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();

44、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 示例 说明 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。 / 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.