[Inno Setup] 字符串列表,当要处理一长串文件时很有用
https://wiki.freepascal.org/TStringList-TStrings_Tutorial
TStringList-TStrings Tutorial
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Contents
TStringList
The TStringList (or its parent TStrings) is much like a fancy dynamic array or Set of Strings (a set of strings is not possible in FPC). It will come in handy a lot when programming and I'm going to teach you basic TStringList usage!
Simple example
program StrList;
{$mode objfpc}
uses
Classes, SysUtils;
var
Str: TStringList;
begin
Str := TStringList.Create; // This is needed when using this class(or most classes)
Str.Add('Some String!');
writeln('The stringlist now has ' + IntToStr(Str.Count) + ' string(s).');
Readln;
Str.Free; //Release the memory used by this stringlist instance
end.
This is a simple console program that will create and add one string to a stringlist. Now here's some things you should know:
Create - Will create the string list for modifying. If you use Create, you have to later Free it and release the memory it takes. If not, you program will not crash, but it will not release all the memory it occupied: a memory leak.
Count - This property is a counter for the number of strings in the List.
Add - This method allows you to add one string to the stringlist. It is a function that will return the Index of the String. This is where the counter comes in handy.
Delete - Will delete a string from the stringlist. Just know that you do not simply input the string, you have to input the index of the string. Like I said: it's like a fancy Dynamic Array.
IndexOf - Will return the index of the string in the list. If it is not found it returns -1.
Clear - Will clear the list.
Expanded Example
How about a more juicy example, eh?
program StrList2;
{$mode ObjFPC}
uses
Classes, SysUtils;
var
Str: TStringList;
S: String;
Counter: Integer;
begin
Str := TStringList.Create;
Writeln('String List Test');
repeat
Writeln('Enter a string to add (type EXIT to stop adding strings)');
Readln(S);
if (S = 'EXIT') then
Break; // exit the loop
if (S <> '') then
begin
Counter := Str.Add(S);
Writeln('String: ' + S + ' was Added!');
Writeln('Index is: ' + IntToStr(Counter)); // The counter will always become the index of the last thing added
end
else
begin
Writeln('No data entered...');
end;
until (S = 'EXIT');
writeln('Contents of the TStringList: '+ Str.CommaText);
Str.Free; //release the memory again
end.
However, to avoid possible memory leaks you should always use a Try - Finally block where possible for this, so you get something like:
var
slist: TStringList;
...
slist := TStringList.Create;
try
...
// do things with your stringlist
...
finally
if Assigned(slist) then
FreeAndNil(slist);
end;
// This works perfect, no double creation of stringlist... comments free to send to edgarrod71@gmail.com
function theStringList: TStringList;
var
J: integer;
begin
result := TStringList.Create;
for J:=0 to 10 do
result.add(intToStr(J));
end;
procedure Caller;
var
SL: TStringList;
K: integer;
begin
SL := theStringList;
for K:=0 to pred(SL.Count) do
writeln(SL[K]);
if assigned(SL) then
SL.Free;
end;
Conversion to and from delimited strings
Code below will result in a stringlist, containing 4 elements ('1', '2', '3' and '4');
procedure Sample;
var
MyStringList: TStringList=nil;
begin
MyStringList:= TStringList.create;
MyStringList.Delimiter := ';';
MyStringList.DelimitedText:='1;2;3;4';
MyStringList.free;
end;
Respectively next code will assemble a stringlist into a delimited string ('1;2;3;4'):
function Sample2 : string;
var
MyStringList: TStringList=nil;
begin
MyStringList:= TStringList.create;
MyStringList.Delimiter := ';';
MyStringList.Add('1');
MyStringList.Add('2');
MyStringList.Add('3');
MyStringList.Add('4');
Result :=MyStringList.DelimitedText;
MyStringList.free;
end;
Note that Delimter is a character, not a string!
If your separator is a string (for example „\n‟), you could use code
below, to get a stringlist, containing 4 elements ('1', '2', '3' and
'4'):
procedure Sample;
var
MyStringList: TStringList=nil;
begin
MyStringList:= TStringList.create;
MyStringList.text:=StringReplace('1\n2\n3\n4','\n',Lineending,[rfReplaceAll, rfIgnoreCase]);
MyStringList.free;
end;
Vice versa, next function will return „1\n2\n3‟:
Function Sample : string;
var
MyStringList: TStringList=nil;
begin
MyStringList:= TStringList.create;
MyStringList.SkipLastLineBreak := True;
MyStringList.add('1');
MyStringList.add('2');
MyStringList.add('3');
result := StringReplace(MyStringList.Text,Lineending,'\n', [rfReplaceAll, rfIgnoreCase]);
MyStringList.free;
end;
File Handling
When using the TStringList you have 2 file handling procedures: SaveToFile and LoadFromFile. SavetoFile will save all strings in the list to a file. LoadFromFile will open the file and add the file data to the list string by string.
program StrListFile;
{$mode objfpc}
uses
Classes, SysUtils;
var
Str: TStringList;
begin
Str := TStringList.Create;
try
Str.LoadFromFile('SomeFile.txt');
Str.Add('Hello');
Str.SaveToFile('SomeFile.txt');
finally
Str.Free;
end;
end.
You just opened a file, edited it and saved it right back to were it was!
Dynamic string array comparison
TStringList is simply an object-oriented version of a dynamic string array. Some methods have analogs:
Operation | array of string | TStringList |
---|---|---|
Variable declaration | StringList: array of string; | StringList: TStringList; |
Initialization | implicit constructor | StringList := TStringList.Create |
Set size | SetLength(StringList, X); | StringList.Size := X; |
Get size | X := Length(StringList); | X := StringList.Count; |
Add item | SetLength(StringList, Length(StringList) + 1); StringList[Length(StringList) - 1] := X; | StringList.Add(X); |
Delete item | for I := Index to Length(StringList) - 2 do StringList[I] := StringList[I + 1]; SetLength(StringList, Length(StringList) - 1); | StringList.Delete(Index); |
Remove all items | SetLength(StringList, 0); | StringList.Clear; |
Finalization | implicit destructor | StringList.Free; |
However, TStringList offers much more functionality than a basic structure such as a dynamic array.
Keep Learning
TStringList has many other interesting features:
- It allows you to sort the strings
- It allows you to limit the list to only unique strings
- You can get the text of all strings as a single string using the Text property.
- You can store an object or other data next to the string
You can learn all the different procedures, functions and properties. See TStringList documentation... or the help in Lazarus.
... and you might like to extend this tutorial if you feel like it.