Question

文件中存储的四个数字以ASCII写入，并用“空格”分隔。如何将它们读为整数？

示例文件：

53545153 49575150 56485654 53565257 52555756 51534850 56575356 56505055 55525453

这是我尝试过的：

ifstream infile("afile2.txt");
if (infile.is_open()) 
{
    string str2;
    char c;
    while (!infile.eof())
    {
        getline(infile, str2, ' ');

        for (std::string::iterator it = str2.begin(); it != str2.end(); ++it)
            cout << (char)*it;
        cout << " ";


    }
}
infile.close();

在上面的代码中，(char)*it仅选择第一位数字，而ASCII码从2位数字开始，即48。

Answer 1

文件中存储的四个数字以ASCII格式写入，并用“空格”分隔。如何将它们读取为整数。示例文件：53545153 49575150 56485654 53565257 52555756 51534850 56575356 56505055 55525453

看起来像8位数字。

要从文件中读取以空格分隔的数字，只需将operator>>从流中转换为整数。

int value;
if (stream >> value) {
    // Successfully read a number.
}

如果要从文件中读取所有值。您可以使用循环：

int value;
while (stream >> value) {
    // Enter the body of the loop each time a number is read.
}

注意：您对eof（）的使用不当：

while (!infile.eof()) {
    // If you enter here the file may be open and readable
    // BUT there may be no data left in the file and thus the next
    // attempt to read will fail if there is no data.
    //
    // This happens because the last successful read will read up-to
    // but not past the EOF. So you have read all the data but not read
    // past the EOF so eof() will return false.
}

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那么我们如何从8个大数字分隔的组中读取2个数字。

好吧，我们想使其像标准流读取一样工作，因此我们仍然想使用operator>>从流中读取。但是，没有任何内置类型读取两位数字。因此，我们需要定义自己的类，该类将读取两位数字。

 struct TwoDigit
 {
     int    value;                  // store the result here
     operator int() {return value;} // Convert TwoDigit to integer
 };
 std::ostream& operator<<(std::ostream& str, TwoDigit const& data) {
     str << data.value; // You can do something more complicated
                        // for printing but its not the current question
                        // so I am just going to dump the value out.
 }
 std::istream& operator>>(std::istream& str, TwoDigit& data) {
     char c1 = 'X';
     char c2 = 'Y';

     if (str >> c1 >> c2) {
         // successfully read two characters from the stream.
         // Note >> automatically drops white space (space return etc)
         // so we don't need to worry about that.

         if (('0' <= c1 && c1 <= '9') && ('0' <= c2 && c2 <= '9')) {
              // We have all good data.
              // So let us update the vale.
              data.value = ((c1 - '0') * 10) + (c2 - '0');
         }
         else {
              // We have bad data read from the stream.
              // So lets mark the stream as bad;
              str.clear(std::ios::failbit);
         }
    }
    return str;
}

现在在您的代码中，您只需阅读即可

 TwoDigit  data;
 if (stream >> data) {
      // Read a single two digit value correctly.
 }

 // or for a loop:
 while(stream >> data) {
      // Keep reading data from the stream.
      // Each read will consume two digits.
 }

 // or if you want to fill a vector from a stream.
 std::vector<TwoDigit> data(std::istream_iterator<TwoDigit>(stream),
                            std::istream_iterator<TwoDigit>());

 // You can even create a vector of int just as easily.
 // Because the TwoDigit has an `operator int()` to convert to int.
 std::vector<int>      data(std::istream_iterator<TwoDigit>(stream),
                            std::istream_iterator<TwoDigit>());

Answer 2

如果我正确理解了这个问题，这可能是一种方法。

#include <cmath>
#include <iostream>
#include <string>
#include <vector>

std::vector<int> conv(std::istream& is) {
    std::vector<int> retval;

    std::string group;
    while(is >> group) { // read "53545153" for example
        int mul =
            static_cast<int>(std::pow(10, (group.size() / 2) - 1)); // start at 1000

        int res = 0;

        for(size_t i = 0; i < group.size(); i += 2, mul /= 10) {
            // convert "53" to dec ASCII char 53 ('5') and then to an int 5 and
            // multiply by 1000 (mul)
            res += (((group[i] - '0') * 10 + (group[i + 1] - '0')) - '0') * mul;
        }
        retval.emplace_back(res); // store
    }
    return retval;
}

测试功能：

#include <sstream>

int main() {
    std::istringstream is(
        "53545153 49575150 56485654 53565257 52555756 51534850 56575356 56505055 55525453");

    auto r = conv(is);

    for(int x : r) {
        std::cout << x << "\n";
    }
}

输出：

如何将文件中的ASCII码转换为整数

2 个答案:

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