c++ - 程序总是产生相同的值(value)？

Question

我的程序的要点是将数字 1 - 1,000,000 写入文本文件，生成 1 到 1,000,000 之间的随机数，在文本文件中搜索该行，取值，然后对其进行平方(这只是对我来说是一个练习，它没有实际应用)。问题是无论何时我运行它，值都保持不变，但 rand() 函数由 time(0) 播种。我怀疑这是一个垃圾值，但我不知道它来自哪里(我没有使用 GDB 或任何其他独立调试器的经验)。这是我的源代码:

#include <fstream>
#include <ctime>
#include <iostream>
#include <string>
#include <cstdlib>
using namespace std;

int main(int argc, char** argv){
    ofstream file("log.txt", ios::app);
    ofstream programLog("programlog.dat", ios::app);
    cout << "Test Start" << endl;
    programLog << "Test Start" << endl;
    cout << "Log file created" << endl;
    programLog << "Log file created" << endl;
    ifstream readFile("log.txt");
    int foundNum;
    std::string line = "";
    unsigned int loopCount = 1000000;
    unsigned int numToSearch;
    const unsigned short min = 1;
    const int max = 1000000;
    unsigned int randomLine = 0;

    for(int i = 0; i <= loopCount; i++){
        file << i << endl;
    }

    //select random line
    srand((unsigned)time(0));

    while(!(randomLine > min) && !(randomLine < max)){
        randomLine = (unsigned)rand();
        programLog << randomLine;
        int newlines = 0;
        //size_t found;
        while(getline(readFile, line)){
            if(line.find("\n") != string::npos)
                newlines++;
            if(newlines == randomLine)
                numToSearch = atoi(line.c_str());
        }

    }

    programLog << "Random line selected" << endl;

    //read line
    while(std::getline(readFile,line)){
        if(atoi(line.c_str()) == numToSearch){
            foundNum = numToSearch;
            break;
        }
        else
            continue;
    }

    //square it
    const unsigned int squared = foundNum*foundNum;

    programLog << squared;
    readFile.close(); //end read
    file.close(); //end log
    programLog.close(); //end programlog
    return 0;
}

Answer 1

您永远不会在使用时进入 while 循环:

while(!(randomLine > min) && !(randomLine < max))

while 立即评估为 false。你应该使用:

while(randomLine < min || randomLine > max)

还有，为什么你所有的变量都有不同的类型？这可能会导致意外错误。您应该将它们更改为相同的类型。