string types

delphi2007

1、有3种类型的字符串

    ShortString：255个字符

    AnsiString：表示8位的ansi，DBCS ANSI，MBCS ANSI等。也称为长字符串。

    WideString：表示Unicode；可用于多用户服务、多种语言应用程序。

这三种字符串可以在赋值和表达式等各种操作中混用，也就是说编译器会自动进行这三种之间的类型转换。

Win32平台系统默认为AnsiString。

2、AnsiString

    该类型的变量是一个4字节指针，指向包含字符串内容的在堆上动态分配的内存块。该内存块的前8个字节中，前2个字节记录字符串长度，后2个字节记录引用数量。生存期自管理。

  copy-on-write：当且仅当字符串的引用计数大于1时，如果字符串中任意字符发生变化，那么就产生一个新的字符的副本。

  Char、PChar，AnsiChar，PAnsiChar，AnsiString这几个类型实现对单字节或多字节字符的支持。

  注意：通过S[i]这种方式来访问第i个字符是不靠谱的，应使用相应的方法，大多以Ansi开头的。

 3、WideString

    表示unicode格式的字符串。WideChar，PWideChar，WideString。

    WideString不是引用计数的，但生命周期是自管理的！

4、null结尾的字符串

  用指针方式声明的字符串，都以null（#0）为结束字符。可以通过强转为string，实现字符串常见操作，如2个字符串的连接等。

5、Null-terminated string functions  

Function	Description
StrAlloc	Allocates a character buffer of a given size on the heap.
StrBufSize	Returns the size of a character buffer allocated using StrAlloc or StrNew.
StrCat	Concatenates two strings.
StrComp	Compares two strings.
StrCopy	Copies a string.
StrDispose	Disposes a character buffer allocated using StrAlloc or StrNew.
StrECopy	Copies a string and returns a pointer to the end of the string.
StrEnd	Returns a pointer to the end of a string.
StrFmt	Formats one or more values into a string.
StrIComp	Compares two strings without case sensitivity.
StrLCat	Concatenates two strings with a given maximum length of the resulting string.
StrLComp	Compares two strings for a given maximum length.
StrLCopy	Copies a string up to a given maximum length.
StrLen	Returns the length of a string.
StrLFmt	Formats one or more values into a string with a given maximum length.
StrLIComp	Compares two strings for a given maximum length without case sensitivity.
StrLower	Converts a string to lowercase.
StrMove	Moves a block of characters from one string to another.
StrNew	Allocates a string on the heap.
StrPCopy	Copies a Pascal string to a null-terminated string.
StrPLCopy	Copies a Pascal string to a null-terminated string with a given maximum length.
StrPos	Returns a pointer to the first occurrence of a given substring within a string.
StrRScan	Returns a pointer to the last occurrence of a given character within a string.
StrScan	Returns a pointer to the first occurrence of a given character within a string.
StrUpper	Converts a string to uppercase.

这些标准函数都可以处理多字节格式的字符串，同Ansi-函数。