delphi字符函数Copy,Pos,Quotedstr

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Pos function
   Returns the index value of the first character in a specified substring that occurs in a given string.

Unit
System

Category
string handling routines
function Pos(Substr: string; S: string): Integer;

Description
Pos searches for a substring, Substr, in a string, S. Substr and S are string-type expressions.

Pos searches for Substr within S and returns an integer value that is the index of the first character of Substr within S. Pos is case-sensitive. If Substr is not found, Pos returns zero.If the substr located at the first place, then return 1;

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Copy function
Returns a substring of a string or a segment of a dynamic array.

Unit
System

Category
string handling routines
function Copy(S; Index, Count: Integer): string;
function Copy(S; Index, Count: Integer): array;

Description
S is an expression of a string or dynamic-array type. Index and Count are integer-type expressions. Copy returns a substring or sub array containing Count characters or elements starting at S[Index]. 

If Index is larger than the length of S, Copy returns an empty string or array.
If Count specifies more characters or array elements than are available, only the characters or elements from S[Index] to the end of S are returned.

Note: When S is a dynamic array, Copy can only be used as a parameter in a call to a procedure or function that expects an array parameter. That is, it acts like the Slice function when working with dynamic arrays.
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QuotedStr function
Returns the quoted version of a string.

Unit
SysUtils

Category
String handling routines
function QuotedStr(const S: string): string;

Description
Use QuotedStr to convert the string S to a quoted string. A single quote character (‘) is inserted at the beginning and end of S, and each single quote character in the string is repeated.

Note: When working with multi-byte character systems (MBCS), use AnsiQuotedStr instead.