https://msdn.microsoft.com/zh-cn/aa315043

1、字符串提取函数，CString::Left、CString::Mid 、CString::Right

CString::Mid

CString Mid( int nFirst ) const; throw( CMemoryException );

CString Mid( int nFirst, int nCount ) const; throw( CMemoryException );

Return Value

A CString object that contains a copy of the specified range of characters. Note that the returned CString object may be empty.

Parameters

nFirst

The zero-based index of the first character in this CString object that is to be included in the extracted substring.

nCount

The number of characters to extract from this CString object. If this parameter is not supplied, then the remainder of the string is extracted.

Remarks

Extracts a substring of length nCount characters from this CString object, starting at position nFirst (zero-based). The function returns a copy of the extracted substring. Mid is similar to the Basic MID$ function (except that indexes are zero-based).

For multibyte character sets (MBCS), nCount refers to each 8-bit character; that is, a lead and trail byte in one multibyte character are counted as two characters.

Example

The following example demonstrates the use of CString::Mid.

// example for CString::Mid
CString s( _T("abcdef") );
ASSERT( s.Mid( 2, 3 ) == _T("cde") );

CString::Left

CString Left( int nCount ) const; throw( CMemoryException );

Return Value

A CString object containing a copy of the specified range of characters. Note that the returned CString object may be empty.

Parameters

nCount

The number of characters to extract from this CString object.

Remarks

Extracts the first (that is, leftmost) nCount characters from this CString object and returns a copy of the extracted substring. If nCount exceeds the string length, then the entire string is extracted. Left is similar to the Basic LEFT$ function (except that indexes are zero-based).

For multibyte character sets (MBCS), nCount refers to each 8-bit character; that is, a lead and trail byte in one multibyte character are counted as two characters.

Example

The following example demonstrates the use of CString::Left.

// example for CString::Left
CString s( _T("abcdef") );
ASSERT( s.Left(2) == _T("ab") );

CString::Right

CString Right( int nCount ) const; throw( CMemoryException );

Return Value

A CString object that contains a copy of the specified range of characters. Note that the returned CString object may be empty.

Parameters

nCount

The number of characters to extract from this CString object.

Remarks

Extracts the last (that is, rightmost) nCount characters from this CString object and returns a copy of the extracted substring. If nCount exceeds the string length, then the entire string is extracted. Right is similar to the Basic RIGHT$ function (except that indexes are zero-based).

For multibyte character sets (MBCS), nCount refers to each 8-bit character; that is, a lead and trail byte in one multibyte character are counted as two characters.

Example

The following example demonstrates the use of CString::Right.

// example for CString::Right
CString s( _T("abcdef") );
ASSERT( s.Right(2) == _T("ef") );