FillMemory、ZeroMemory 一目了然的兩個(gè)函數(shù), 但其實(shí)它們都是調(diào)用了 FillChar;
清空不過(guò)就是填充空字符(#0: 編號(hào)為 0 的字符), 說(shuō)來(lái)說(shuō)去是一回事.
為了下面的測(cè)試, 先寫(xiě)一個(gè)以十六進(jìn)制方式查看內(nèi)存的函數(shù):
function GetMemBytes(var X; size: Integer): string;
var
pb: PByte;
i: Integer;
begin
pb := PByte(X);
for i := 0 to size - 1 do
begin
Result := Result + IntToHex(pb^, 2) + #32;
Inc(pb);
end;
end; {GetMemBytes end}
//測(cè)試:
var
p1: PAnsiChar;
p2: PWideChar;
s1: AnsiString;
s2: UnicodeString;
begin
p1 := 'ABCD';
p2 := 'ABCD';
s1 := 'ABCD';
s2 := 'ABCD';
ShowMessage(GetMemBytes(p1,4)); {41 42 43 44}
ShowMessage(GetMemBytes(p2,8)); {41 00 42 00 43 00 44 00}
ShowMessage(GetMemBytes(s1,4)); {41 42 43 44}
ShowMessage(GetMemBytes(s2,8)); {41 00 42 00 43 00 44 00}
end;
測(cè)試 FillMemory、ZeroMemory、FillChar 三個(gè)填充函數(shù):
const
num = 10;
var
p: PChar;
begin
p := StrAlloc(num);
ShowMessage(GetMemBytes(p, num)); {從結(jié)果看出 StrAlloc 沒(méi)有初始化內(nèi)存}
FillMemory(p, num, Byte('A'));
ShowMessage(GetMemBytes(p, num)); {41 41 41 41 41 41 41 41 41 41}
ZeroMemory(p, num);
ShowMessage(GetMemBytes(p, num)); {00 00 00 00 00 00 00 00 00 00}
FillChar(p^, num, 'B');
ShowMessage(GetMemBytes(p, num)); {42 42 42 42 42 42 42 42 42 42}
StrDispose(p);
end;
此時(shí), 我想到一個(gè)問(wèn)題:
GetMem 和 GetMemory 沒(méi)有初始化內(nèi)存; AllocMem 會(huì)初始化內(nèi)存為空, 那么
ReallocMem、ReallocMemory 會(huì)不會(huì)初始化內(nèi)存?
測(cè)試一下(結(jié)果是沒(méi)有初始化):
{測(cè)試1}
var
p: Pointer;
begin
p := GetMemory(3);
ShowMessage(GetMemBytes(p, 3));
ReallocMem(p, 10);
ShowMessage(GetMemBytes(p, 10)); {沒(méi)有初始化}
FreeMemory(p);
end;
{測(cè)試2}
var
p: Pointer;
begin
p := AllocMem(3);
ShowMessage(GetMemBytes(p, 3));
ReallocMem(p, 10);
ShowMessage(GetMemBytes(p, 10)); {沒(méi)有初始化}
FreeMemory(p);
end;
另外: FillMemory、ZeroMemory 的操作對(duì)象是指針, 而 FillChar 的操作對(duì)象則是實(shí)體.
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