Delphi 的内存操作函数(4): 清空与填充内存

 FillMemory、ZeroMemory 一目了然的两个函数, 但其实它们都是调用了 FillChar;

清空不过就是填充空字符(#0: 编号为 0 的字符), 说来说去是一回事.

为了下面的测试, 先写一个以十六进制方式查看内存的函数:

---

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}

//测试:

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;

 

---

测试 FillMemory、ZeroMemory、FillChar 三个填充函数:

---

const

  num = 10;

var

  p: PChar;

begin

  p := StrAlloc(num);

  ShowMessage(GetMemBytes(p, num)); {从结果看出 StrAlloc 没有初始化内存}

  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;

 

---

此时, 我想到一个问题: 

GetMem 和 GetMemory 没有初始化内存; AllocMem 会初始化内存为空, 那么

ReallocMem、ReallocMemory 会不会初始化内存?

测试一下(结果是没有初始化):

---

{测试1}.

var

  p: Pointer;

begin

  p := GetMemory(3);

  ShowMessage(GetMemBytes(p, 3));

  ReallocMem(p, 10);

  ShowMessage(GetMemBytes(p, 10)); {没有初始化}

  FreeMemory(p);

end;

{测试2}

var

  p: Pointer;

begin

  p := AllocMem(3);

  ShowMessage(GetMemBytes(p, 3));

  ReallocMem(p, 10);

  ShowMessage(GetMemBytes(p, 10)); {没有初始化}

  FreeMemory(p);

end;

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另外: FillMemory、ZeroMemory 的操作对象是指针, 而 FillChar 的操作对象则是实体.