An induction (original) of the string problem during windows program development by VC)

The first problem for beginners in Windows development is to understand the strings.

I. Brief History of character sets

A character is a concept independent of a computer. Without a computer, there are still characters, characters are character symbols, English, Chinese, and Japanese.

A string is an array of characters.

Previously, the computer used a single byte to represent a single character. byte is an 8-bit unsigned number. The single-byte ASCII code can represent uppercase and lowercase English and some punctuation marks.

Later, in order to display Chinese characters, Japanese characters and other Asian characters, the dual-byte encoding was developed, using two or one byte to represent a character.

AndCodePage, two bytes in different code pages, the characters are also different, the simplified Chinese code page is GBK, the traditional Chinese is big5, and so on.

In such a string, there are both single-byte characters and double-byte characters, it is difficult to count the number of characters in a string.

Then there is Unicode, Unicode encoding system in the UTF-16 standard, the provisions will use two bytes to represent a character, this can represent the characters in various languages in the world, do not need to distinguish the code page, they have their own 16-bit encoding in the UTF-16 coding system, although the storage space is increased, but the efficiency is obviously improved.

2. Various string processing function libraries

1 C Runtime Library processing strings:

Str * series: The C Runtime uses strlen strcpy and other Str * series functions to process char strings.
WCS * series: After the C compiler has the built-in wchar_t 16-bit wide byte type, use the new wcslen wcscpy and other functions of the WCS * series to process the wchar_t type strings.
_ TCS * series: The C Runtime Library defines macro definitions of _ tcslen _ tcscpy and other _ TCS * series, during compilation, the _ TCS * series functions are determined based on whether macro _ Unicode is predefined. Otherwise, the * series functions are used.

_ TCS * _ S Series: The latest secure string functions of the C Runtime Library. New functions are defined to prevent Buffer Overflow.

2. The windows development team processes strings:

Windows development team in winnt. h defines the new data types char (char), wchar (wchar_t), tchar, and tchar. during compilation, determine whether the Unicode macro is predefined or not to determine whether it is Char or wchar.

Lstr * A Series: defined in kernel32.dll of the Windows operating system. Processing char strings is actually a layer of packaging for lstr * w.
Lstr * W series: It is defined in kernel32.dll of Windows operating system to process string of the wchar type.
Lstr * series: lstr * series functions are also used to determine whether to use the lstr * a series functions or the lstr * W series functions based on whether Unicode macros are predefined during compilation.

In fact, I usually use the lstr * series, because it is written by the Windows API.ProgramYou do not need to link the C Runtime Library.

Note that the _ Unicode and Windows Unicode macros of the C Runtime Library are either defined at the same time or not defined at the same time. The prefix underline Of the C Runtime library is used to comply with the damn C ++ standard (for macros that do not belong to the C ++ standard with underscores), while Windows does not comply with that standard.

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Although the string processing looks messy, it is enough to grasp a single application. Although the currently recommended standard is the _ TCS * _ S series, you can use it as needed, the string type in STL library and MFC library is not introduced, because the two libraries are c ++ library, not C library.