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