Conversion of common data types in Visual C ++

I haven't used C ++ for a long time. It's not very easy to do. Data type conversion is really not as convenient as C ......
From: Skynet
The conversion of common data types is as follows:

Int I = 100; Long L = 2001; Float F = 300.2; Double D = 12345.119; Char username [] = "Woman 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 );

2. Obtain the pointer to the string from other variables containing the string

Cstring variable

STR = "2008 Beijing Olympics "; Buf = (lpstr) (lpctstr) STR;

_ Variant_t variable of the BSTR type

V1 = (_ bstr_t )"ProgramMember "; Buf = _ com_util: convertbstrtostring (_ bstr_t) V1 );

Iii. 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 );

4. 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;

V. BSTR, _ bstr_t and ccombstr

Ccombstr and _ bstr_t are encapsulation of BSTR, and BSTR is a 32-bit pointer to a string.

Char * can be converted to BSTR like this: bstr B = _ com_util: convertstringtobstr ("data"); // you need to add the header file comutil. h before use

Otherwise, you can use

Char * P = _ com_util: convertbstrtostring (B );

6. 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

For variant that is not immediately assigned a value, it is best to initialize with void variantinit (variantarg far * pvarg); in essence, the VT is set to vt_empty, the following table lists the correspondence between VT and common data:

Unsigned char bval; vt_ui1 Short ival; vt_i2 Long lval; vt_i4 Float fltval; vt_r4 Double dblval; vt_r8 Variant_bool boolval; vt_bool Scode; vt_error Cy cyval; vt_cy Date; vt_date BSTR bstrval; vt_bstr Iunknown far * punkval; vt_unknown Idispatch far * pdispval; vt_dispatch Safearray far * parray; vt_array | * Unsigned char far * pbval; vt_byref | vt_ui1 Short far * pival; vt_byref | vt_i2 Long far * plval; vt_byref | vt_i4 Float far * pfltval; vt_byref | vt_r4 Double far * pdblval; vt_byref | vt_r8 Variant_bool far * pboolval; vt_byref | vt_bool Scode far * pscode; vt_byref | vt_error Cy far * pcyval; vt_byref | vt_cy Date far * pdate; vt_byref | vt_date BSTR far * pbstrval; vt_byref | vt_bstr Iunknown far * ppunkval; vt_byref | vt_unknown Idispatch far * ppdispval; vt_byref | vt_dispatch Safearray far * pparray; vt_array | * Variant far * pvarval; vt_byref | vt_variant Void far * byref; vt_byref

_ 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.

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;

VII. Others

During message processing, we often need to split wparam, lparam, and other 32-bit data (DWORD) into two 16-bit data (Word), for example:

Lparam; Word lovalue = loword (lparam); // take 16 bits Word hivalue = hiword (lparam); // you can specify 16 characters in height.

For a 16-bit data (Word), we can use the same method to break down the high and low 8-bit data (byte), for example:

Word wvalue; Byte lovalue = lobyte (wvalue); // get 8 bits Byte hivalue = hibyte (wvalue); // get the 8-bit high