c++ - 为什么 C++ 从 txt 文件中读取错误的值？

Question

我做了一个程序，从txt文件“database.txt”中读取值，但是当数字是三位数时输出错误

ifstream myfile("database.txt");
int broj_rijeci = 0;
if (myfile.is_open())
{
    while (getline(myfile, line))
    {
        if (line.at(0) == '[')
        {
            int i = line.length() - 2;
            int brojac = 0;
            system("pause");
            while (line.at(i) != line.at(0))
            {
                input = line.at(i);
                ascii_convert(input);
                broj_rijeci = broj_rijeci + input * pow(10, brojac);
                i--;
                brojac++;
            }
        }
    }
    myfile.close();
}
else cout << "Unable to open file";

我的数据库是这样的:

[311]

输出为“310”

Answer 1

由于您没有提供 ascii_convert 的实现，因此很难判断问题出在何处还是在其他地方。但是，通过使用 std::stringstream，您可以大大简化该过程并消除对您自己的转换例程的需要。

#include <sstream>

std::ifstream myfile("database.txt");
if (myfile.is_open())
{
    std::string line;
    while (std::getline(myfile, line))
    {
        if (line.size() > 1 && line[0] == '[' && line[line.size() - 1] == ']')
        {
            int value;
            if(std::istringstream(line.substr(1, line.size() - 2)) >> value)
            {
                // Conversion was a success ... do something with "value"
            }
            else
            {
                // Conversion failed. Handle error condition.
            }
        }
    }
    myfile.close();
}
else std::cout << "Unable to open file";