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
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Function
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Description
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StrAlloc
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Allocates a character buffer of a given size on the heap.
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StrBufSize
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Returns the size of a character buffer allocated using StrAlloc or StrNew.
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StrCat
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Concatenates two strings.
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StrComp
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Compares two strings.
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StrCopy
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Copies a string.
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StrDispose
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Disposes a character buffer allocated using StrAlloc or StrNew.
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StrECopy
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Copies a string and returns a pointer to the end of the string.
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StrEnd
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Returns a pointer to the end of a string.
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StrFmt
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Formats one or more values into a string.
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StrIComp
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Compares two strings without case sensitivity.
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StrLCat
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Concatenates two strings with a given maximum length of the resulting string.
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StrLComp
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Compares two strings for a given maximum length.
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StrLCopy
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Copies a string up to a given maximum length.
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StrLen
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Returns the length of a string.
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StrLFmt
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Formats one or more values into a string with a given maximum length.
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StrLIComp
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Compares two strings for a given maximum length without case sensitivity.
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StrLower
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Converts a string to lowercase.
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StrMove
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Moves a block of characters from one string to another.
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StrNew
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Allocates a string on the heap.
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StrPCopy
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Copies a Pascal string to a null-terminated string.
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StrPLCopy
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Copies a Pascal string to a null-terminated string with a given maximum length.
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StrPos
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Returns a pointer to the first occurrence of a given substring within a string.
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StrRScan
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Returns a pointer to the last occurrence of a given character within a string.
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StrScan
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Returns a pointer to the first occurrence of a given character within a string.
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StrUpper
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Converts a string to uppercase.
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这些标准函数都可以处理多字节格式的字符串，同Ansi-函数。