测试代码:
procedure TForm1.btnXClick(Sender: TObject);
var
xx, yy: array [0..6] of Char; // 内容存在栈里
a: array of Char; // 内容存在堆里,这就可以理解为什么动态数组a代表的是字符串的指针了
begin
SetLength(a, 10);
FillChar(xx, 7, #0);
xx := 'abcdef';
a[0]:='A';
a[1]:='B';
Move(xx, yy, 4);
Move(xx[0], yy[0], 4);
Move(xx,a[0],4);
end;
注释一下Move
procedure Move( const Source; var Dest; count : Integer );
{$IFDEF PUREPASCAL}
var
S, D: PChar;
I: Integer;
begin
S := PChar(@Source);
D := PChar(@Dest);
if S = D then Exit;
if Cardinal(D) > Cardinal(S) then //精华1:小心,别覆盖了Source
for I := count-1 downto 0 do
D[I] := S[I]
else
for I := 0 to count-1 do
D[I] := S[I];
end;
{$ELSE}
asm
{ ->EAX Pointer to source }
{ EDX Pointer to destination }
{ ECX Count }
PUSH ESI
PUSH EDI
MOV ESI,EAX
MOV EDI,EDX
MOV EAX,ECX
CMP EDI,ESI
JA @@down
JE @@exit
SAR ECX,2 { copy count DIV 4 dwords }
JS @@exit
REP MOVSD
MOV ECX,EAX //精华2: 放之四海皆准。
AND ECX,03H
REP MOVSB { copy count MOD 4 bytes }
JMP @@exit
@@down:
LEA ESI,[ESI+ECX-4] { point ESI to last dword of source }
LEA EDI,[EDI+ECX-4] { point EDI to last dword of dest }
SAR ECX,2 { copy count DIV 4 dwords }
JS @@exit
STD
REP MOVSD
MOV ECX,EAX
AND ECX,03H { copy count MOD 4 bytes }
ADD ESI,4-1 { point to last byte of rest }
ADD EDI,4-1
REP MOVSB
CLD
@@exit:
POP EDI
POP ESI
end;
{$ENDIF}
