如何避免警告C4244：从'ULONGLONG'转换为"双倍"，可能丢失数据

How can avoid warning C4244: conversion from 'ULONGLONG' to 'double', possible loss of data

本文关键字：双倍 数据 ULONGLONG C4244 警告 何避免 转换      更新时间：2023-10-16

我使用的是Win32 x64环境

也请转到下面的链接

我已经从这个链接找到了答案收集进程的CPU使用情况

在Windows标准的第一个答案下，您可以看到如下代码片段：

double getCurrentValue(){
FILETIME ftime, fsys, fuser;
ULARGE_INTEGER now, sys, user;
double percent;
GetSystemTimeAsFileTime(&ftime);
memcpy(&now, &ftime, sizeof(FILETIME));
GetProcessTimes(self, &ftime, &ftime, &fsys, &fuser);
memcpy(&sys, &fsys, sizeof(FILETIME));
memcpy(&user, &fuser, sizeof(FILETIME));
percent = (sys.QuadPart - lastSysCPU.QuadPart) +
(user.QuadPart - lastUserCPU.QuadPart);
percent /= (now.QuadPart - lastCPU.QuadPart);
percent /= numProcessors;
lastCPU = now;
lastUserCPU = user;
lastSysCPU = sys;
return percent * 100;
}
//--------------------------- FOCUS -----------------------------//
percent = (sys.QuadPart - lastSysCPU.QuadPart) +(user.QuadPart - lastUserCPU.QuadPart); // ---(1)
percent /= (now.QuadPart - lastCPU.QuadPart); // ---(2)
percent /= numProcessors; // --- (3)

如第行(1)将ULONGLONG(无符号长-长)赋值给双给定编译器warning C4244: conversion from 'ULONGLONG' to 'double', possible loss of data

  • 因此@Line#(1)，(2)&(3)如何保证double precent数据的值

(由于Ulonglong 64位积分数据转换为64位浮点数据)

  • 有时此precent值的值会超过10.00作为CPU使用率的时间戳

假设您在短时间内调用getCurrentValue函数，则可以安全地将值强制转换为两倍。您还可以通过按年份分隔的通话来检查极端情况。

ULONGLONG used = (sys.QuadPart - lastSysCPU.QuadPart) + (user.QuadPart - lastUserCPU.QuadPart);
ULONGLONG elapsed = (now.QuadPart - lastCPU.QuadPart);
if ( elapsed == 0 )
{
// Now it is imposible, but it could be problem in future :)
// Do something sane here. For example restart calculation.
}
else
{
double percent = ( (double)used / (double)elapsed ) / numProcessors * 100.0;
// Clamp value for rounding errors in our or system code.
if ( percent > 100.0 )
percent = 100.0;
if ( elapsed >= ( 1ull << 53 ) || used >= ( 1ull << 53 ) )
{
// Set some flag that result could be not precise.
// For 'elapsed' this needs 28 years.
// 'used' could kick earlier: 28/num_processors years.
// But if you realy need only 4 or 5 digits you can
// ignore this case.
}
}
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