c++ - 写入超过1GB的.txt文件时的奇怪行为

Question

我有一些找到素数的代码，它将这些数字输出到一个.txt文件中，这似乎可以正常工作，直到达到1GB(我不确定确切的文件大小，但它在此范围内)。达到1GB后，文件大小似乎会迅速扩展，我相信这是因为整个数字块都在重复。这是我的代码:

#include "pch.h"
#include <cmath>
#include <fstream>
#include <thread>
#include <iostream>
#include <string>
#include <mutex>

int nextInt = 1;
std::ofstream file;

bool TestPrime(int number)
{
	double rootInt = sqrt(number);
	for (int i = 3; i <= rootInt; i += 2)
	{
		double divValue = (double)number / i;
		if (int(divValue) == divValue)
		{
			return false;
		}
	}
	return true;
}
int GetNextNumber()
{
	static std::mutex m;
	const std::lock_guard<std::mutex> lock(m);
	return (nextInt += 2);
}

void PrimeFinderThread()
{
	while (true)
	{
		int number = GetNextNumber();
		bool isPrime = TestPrime(number);
		if (isPrime)
		{
			std::string fileOutput = std::to_string(number) + "-";
			file << fileOutput;
		}
	}
}

int main() {
	file.open("primes.txt", std::ofstream::app);
	file << "2-";
	std::thread threads[4];
	for (int i = 0; i < 4; i++) {
		threads[i] = std::thread(PrimeFinderThread);
	}
	for (int i = 0; i < 4; i++) {
		threads[i].join();
	}
	return 0;
}

这是.txt文件开头的摘录:

2-3-5-7-11-13-17-19-23-29-31-37-41-43-47-53-59-61-67-71-73-79-83-89-97-101-103-107-109-113-127-131-137-139-149-151-157-163-167-173-179-181-191-193-197-199-211-223-227-229-233-239-241-251-257-263-269-271-277-281-283-293-307-311-313-317-331-337-347-349-353-359-367-373-379-383-389-397-401-409-419-421-431-433-439-443-449-457-461-463-467-479-487-491-499-503-509-521-523-541-547-557-563-569-571-577-587-593-599-601-607-613-617-619-631-641-643-647-653-659-661-673-677-683-691-701

这是文件中间某处的摘录:

2038621267--2038621265--2038621269--2038621263--2038621259--2038621257--2038621255--2038621253--2038621261--2038621249--2038621247--2038621245--2038621367--2038621251--2038621243--2038621237--2038621239--2038621233--2038621231--2038621235--2038621241--2038621227--2038621223--2038621221--2038621219--2038621217--2038621225--2038621213--2038621215--2038621209--2038621207--2038621205--2038621211--2038621203--2038621199--2038621197--2038621229--2038621193--2038621201--2038621189--2038621187--2038621185--2038621183--2038621195

还有文件末尾的一些:

1812147945--1812147959--1812147941--1812147939--1812147947--1812147935--1812147933--1812147937--1812147929--1812147943--1812147925--1812147927--1812147921--1812147919--1812147917--1812147915--1812147913--1812147911--1812147923--1812147909--1812147907--1812147903--1812147901--1812147931--1812147897--1812147895--1812147893--1812147905--1812147889--1812147887--1812147885--1812147899--1812147881--1812147883--1812147891--1812147879--1812147873--1812147871--1812147875--1812147869--1812147865--1812147877--1812147867--1812147859--1812147857--1812147855--1812147853--1812147861

因此，此文件有很多错误:

-There are two dashes sometimes.
-There are numbers at the end of the file that are smaller than the ones in the middle, which should 
 not happen. The numbers may be a bit out of order since it is running on multiple threads, but not 
 by that much.
-if we assume that ever number is 10 digits long, which would mean that they take up 11 bytes each, 
 the largest number it got to was about 2.2 billion. you can estimate the number of primes under that 
 number by using an estimate of the PI function which is π(x) ≈ (x/ln(x)), so the number of primes is 
 about 102 million, so they should take up about 1.1GB of storage. the .txt file is 3.1GB.

有时我会在一段时间后进行文件大小的测量:

10 Minutes : 760MB
20 Minutes : 3.1GB
30 Minutes : 14.6GB

我知道文件大小不是衡量速度的好方法，但是这些值是如此之大，以至于我认为足以表明有问题。

Answer 1

根据我对帖子的原始评论以及OP的回复，看来问题出在数字溢出。一旦数字溢出，您就处于困惑模式。一些数字可能溢出，而另一些尚未溢出，而其他数字可能为负(因此双破折号，因为第二个破折号实际上是减号)