如何从 txt 文件 c++ 中提取括号之间的数字？

Question

我的问题是：我的逻辑有问题。我已经检测到它何时有括号，但现在我需要找到数字并知道它们在 txt 文件中重复了多少次。这是我的 txt 文件：

(Visual basic)
(Llorente)
(Porto, 2008)
(Sommerville, 2010)
References
Visual Basic. (s.f.). Navarra.
Llorente, P.B. (s.f.). Fortran.
Porto, J.P. (2008)
Sommerville, I. (2010). Software Engineering. Unite Kingdom: Pearson.

结果应该是：year : 2008 - 2 times, year : 2010 - 2 times, etc. PD：谢谢我很菜鸟。

#include <regex>
#include <iostream>
#include <fstream>
#include <map>
//33
int main()
{
    std::ifstream readStream("references.txt");
    std::map<int, int> cMap; 
    std::string input;
    std::regex reg(R"(\([a-zA-Z\s]*,?\s*([0-9]+)\))");
    std::regex inte("(\+|-)?[[:digit:]]+");

    ///333
    while (std::getline(readStream, input)) {
            std::match_results < std::string::const_iterator > m;
    if ((std::regex_search(input, m, reg)) ) {
        int year = std::stoi(m[1]); 
        auto value = cMap.find(year);
        if (value != cMap.end()) { 
            cMap[value->first] = value->second + 1;
        } else {
            cMap[year] = 1; 
        }
    }



}
//33
for (auto x : cMap) { 
    std::cout << "year " << x.first << " is - " << x.second << " times." << std::endl;
}
//3
return 0;
}

Answer 1

您可以使用std::regex_search方法来匹配行。但请记住在文件顶部包含 #include <regex>。

#include <regex>
#include <iostream>
#include <fstream>
#include <map>


int main()
{
    std::ifstream readStream("path/to/your/Example.txt");
    std::map<int, int> countMap; // Map containing (year, count) value pairs.
    std::string in;
    std::regex reg(R"(\([a-zA-Z\s]*,?\s*([0-9]+)\))"); // For the regex: \([a-zA-Z\s]*,?\s*([0-9]+)\)

    while (std::getline(readStream, in)) {
        std::match_results < std::string::const_iterator > m;
        if (std::regex_search(in, m, reg)) { // If the current line matches our regex pattern.
            int year = std::stoi(m[1]); // The second element of the array contains our string representing the year.

            auto val = countMap.find(year);
            if (val != countMap.end()) { // If the year is already in the countMap we want to increment it.
                countMap[val->first] = val->second + 1;
            } else {
                countMap[year] = 1; // year doesn't exist in the countMap, it is the first time.
            }
        }
    }

    for (auto x : countMap) { // x is of type std::pair<int, int> which is our (year, count) value pair
        std::cout << "year " << x.first << " is - " << x.second << " times." << std::endl;
    }

    return 0;
}

Answer 2

对于OP的任务，一个简单的循环就可以完成遍历字符串所有字符的工作。从而管理了两种状态：

open ... true 在 '(' 之后和 ')' 之前，否则为 false
number ... true 当找到数字时 open 是 true.

虽然 number 是 true，但会收集并组合成一个 int。如果在 number 为 true 时发现非数字，则这是数字的结尾并存储该值。

数字检查也可以在行尾完成。在这种特定情况下，这意味着语法错误，因为它意味着缺少右括号 ())。（OP 没有说明如何处理这个问题。）

我的示例代码：

#include <iostream>
#include <sstream>
#include <vector>
#include <map>

std::vector<int> parseLine(const std::string &text)
{
  bool open = false, number = false;
  std::vector<int> values; int value = 0;
  for (char c : text) {
    switch (c) {
      case '(': open = true; break;
      case ')': open = false;
      default:
        if (open && c >= '0' && c <= '9') {
          number = true;
          (value *= 10) += (c - '0'); // value = 10 * value + (c - '0')
        } else if (number) {
          values.push_back(value);
          value = 0; number = false;
        }
    }
  }
  if (number) {
    values.push_back(value);
    std::cerr << "ERROR: Missing ')' at line end!\n";
  }
  return values;
}

const std::string text =
"(Visual basic)\n"
"(Llorente)\n"
"(Porto, 2008)\n"
"(Sommerville, 2010)\n"
"References\n"
"Visual Basic. (s.f.). Navarra.\n"
"Llorente, P.B. (s.f.). Fortran.\n"
"Porto, J.P. (2008)\n"
"Sommerville, I. (2010). Software Engineering. Unite Kingdom: Pearson.\n";

int main()
{
  // open file
  std::istringstream in(text);
  // parse/process file line by line
  std::map<int, int> histo;
  for (std::string line; std::getline(in, line);) {
    const std::vector<int> values = parseLine(line);
    // count occurrences of values
    for (int value : values) ++histo[value];
  }
  // report
  std::cout << "Report:\n";
  for (const std::pair<int, int> &entry : histo) {
    std::cout << entry.first << ": " << entry.second << '\n';
  }
  // done
  return 0;
}

输出：

Report:
2008: 2
2010: 2

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如何从 txt 文件 c++ 中提取括号之间的数字？

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