Sort out data type conversion

How to sort out annoying data type conversions

Int I = 100;
Long l = 2001;
Float f = 300.2;
Double d = 12345.119;
Char username [] = "Cheng peijun ";
Char temp [200];
Char * buf;
CString str;
_ Variant_t v1;
_ Bstr_t v2;

1. convert other data types to strings

• Short INTEGER (int)
  
  Itoa (I, temp, 10); // convert I to a string and put it into temp. the last digit indicates decimal.
  Itoa (I, temp, 2); // convert in binary mode
• Long (long)
  
  Ltoa (l, temp, 10 );
• Floating Point Number (float, double)
  
  Fcvt can be used to complete the conversion. This is an example in MSDN:
  Int decimal, sign;
  Char * buffer;
  Double source = 3.1415926535;
  Buffer = _ fcvt (source, 7, & decimal, & sign );
  Running result: source: 3.1415926535 buffer: '20180101' decimal: 1 sign: 0
  Decimal indicates the decimal point position, sign indicates the symbol: 0 is a positive number, and 1 is a negative number.
• CString variable
  
  Str = "2008 Beijing Olympics ";
  Buf = (LPSTR) (LPCTSTR) str;
• BSTR variable
  
  BSTR bstrValue =: SysAllocString (L "programmer ");
  Char * buf = _ com_util: ConvertBSTRToString (bstrValue );
  SysFreeString (bstrValue );
  AfxMessageBox (buf );
  Delete (buf );
• CComBSTR variable
  
  CComBSTR bstrVar ("test ");
  Char * buf = _ com_util: ConvertBSTRToString (bstrVar. m_str );
  AfxMessageBox (buf );
  Delete (buf );
• _ Bstr_t variable
  
  _ Bstr_t is the encapsulation of BSTR. It is easy to use because = operator has been overloaded.
  _ Bstr_t bstrVar ("test ");
  Const char * buf = bstrVar; // do not modify the buf content
  AfxMessageBox (buf );

• General method (for non-COM data types)
  
  Use sprintf to complete the conversion

  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); 

Ii. Convert strings to other data types


Strcpy (temp, "123 ");

• Short INTEGER (int)
  
  I = atoi (temp );
• Long (long)
  
  L = atol (temp );
• Floating Point (double)
  
  D = atof (temp );
• CString variable
  
  CString name = temp;
• BSTR variable
  
  BSTR bstrValue =: SysAllocString (L "programmer ");
  ... // Complete the use of bstrValue
  SysFreeString (bstrValue );
• CComBSTR variable
  
  CComBSTR variables can be directly assigned values.
  CComBSTR bstrVar1 ("test ");
  CComBSTR bstrVar2 (temp );
• _ Bstr_t variable
  
  _ Bstr_t type variables can be directly assigned values
  _ Bstr_t bstrVar1 ("test ");
  _ Bstr_t bstrVar2 (temp );

Iii. convert other data types to CString


Use the CString member function Format for conversion. For example:

• INTEGER (int)
  Str. Format ("% d", I );
• Float)
  Str. Format ("% f", I );
• Data Types supported by CString constructors, such as string pointers (char *), can be directly assigned values.
  Str = username;
• For data types not supported by Format, you can convert the data type to char * by using the method described above, and then assign the value to the CString variable.

Iv. BSTR, _ bstr_t and CComBSTR

• CComBSTR is the encapsulation of BSTR by ATL, _ bstr_t is the encapsulation of BSTR by C ++, and BSTR is a 32-bit pointer, but it does not directly point to the buffer of the string.
  Char * can be converted to BSTR as follows:
  BSTR B = _ com_util: ConvertStringToBSTR ("data"); // comutil. h and comsupp. lib must be added before use.
  SysFreeString (bstrValue );
  Otherwise, you can use
  Char * p = _ com_util: ConvertBSTRToString (B );
  Delete p;
  For details, refer to the specific descriptions in sections 1 and 2.

  CComBSTR and _ bstr_t overload a large number of operators. You can directly perform = ,! =, = And so on, so it is very convenient to use.
  Especially _ bstr_t. We recommend that you use it.

V. VARIANT, _ variant_t, and COleVariant

• For the VARIANT Structure, refer to the definition of the tagVARIANT struct in the header file VC98 \ Include \ OAIDL. H.
  Assign a value to the VARIANT variable: assign a value to the vt member to specify the data type, and then assign a value to the variable of the same data type in the union structure. For example:
  VARIANT va;
  Int a = 2001;
  Va. vt = VT_I4; // specify Integer Data
  Va. lVal = a; // value assignment
• _ Variant_t is the encapsulation class of VARIANT, and its value assignment can be forced type conversion. Its constructor will automatically process these data types.
  # Include <comdef. h> must be added for use.
  For example:
  Long l = 222;
  Ing I = 100;
  _ Variant_t lVal (l );
  LVal = (long) I;
• 
  The use of COleVariant is basically the same as that of the _ variant_t method. See the following example:
  COleVariant v3 = "string", v4 = (long) 1999;
  CString str = (BSTR) v3.pbstrVal;
  Long I = v4.lVal;

  //////////////////////////////////////// //////////////////////////////////////// //////////////////////////////////////// //////////////////

• This topic demonstrates how to convert various C ++ string types to other strings. The string types that can be converted includeChar *,Wchar_t *, _ Bstr_t, CComBSTR, CString, basic_string, and System. String. In all cases, a copy of the string is created when a string is converted to a new type. Any changes made to the new string will not affect the original string, and vice versa.

  Example of conversion from char *

  This example shows howChar *Convert to other string types listed above.

  // 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;}

  Output

  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)

  Example of conversion from wchar_t *

  This example shows howWchar_t *Convert to other string types listed above.

  // 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;}

  Output

  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)

  Example of conversion from _ bstr_t

  This example shows how_ Bstr_tConvert to other string types listed above.

  // 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;}

  Output

  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)

  Example of CComBSTR Conversion

  This example shows howCComBSTRConvert to other string types listed above.

  // 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;}

  Output

  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)

  Example of CString Conversion

  This example shows howCStringConvert to other string types listed above.

  // 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;}

  Output

  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)

  Example of conversion from basic_string

  This example shows howBasic_stringConvert to other string types listed above.

  // 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(){    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;}

  Output

  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)

  Example of conversion from System: String

  This example shows howSystem. StringConvert to other string types listed above.

  // 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;}

  Output

  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)