如何解析文本文件并在C ++中计算重复次数

Question

我正在尝试创建一个C ++程序，从这样的文本文件中获取日志信息：

local - - [24/Oct/1994:13:41:41 -0600] "GET index.html HTTP/1.0" 200 150
local - - [24/Oct/1994:13:41:41 -0600] "GET 1.gif HTTP/1.0" 200 1210
local - - [24/Oct/1994:13:43:13 -0600] "GET index.html HTTP/1.0" 200 3185
local - - [24/Oct/1994:13:43:14 -0600] "GET 2.gif HTTP/1.0" 200 2555
local - - [24/Oct/1994:13:43:15 -0600] "GET 3.gif HTTP/1.0" 200 36403
local - - [24/Oct/1994:13:43:17 -0600] "GET 4.gif HTTP/1.0" 200 441
local - - [24/Oct/1994:13:46:45 -0600] "GET index.html HTTP/1.0" 200 3185

然后我试图获取每行中GET之后的文件名，将其存储在某处并在每次在日志文件中重复文件名时计数。 读完文件后，我打印出前10个重复的文件名。

我的问题是，下面的代码对日志文件中的所有行都计算 - 但这不是我想要的：计算GET和HTTP之间的文件名。

#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>
#include <time.h>
#include <math.h>

const long MAX = 1000000;
std::string words[MAX];
long instances[MAX];
long count = 0;

void insert(std::string input) {
    //check first, add if not present
    for (long i = 0; i < count; i++)
        if (input == words[i]) {
            instances[i]++;
            //std::cout << words[i] << std::endl;
            return;
        }

    if (count < MAX) {
        words[count] = input;
        instances[count] = 1;
        count++;
    }
    else
        std::cerr << "Too many unquie words in the file";
}

long findTop(std::string &word) {
    //int topIndex = 0;
    long topCount = instances[0];
    long topIndex = 0;

    for (long i = 1; i<count; i++)
        if (instances[i] > topCount) {
            topCount = instances[i];
            topIndex = i;
        }
    instances[topIndex] = 0;
    word = words[topIndex];
    //topIndex = i;
    return topCount;
}

long frequency_of_primes(long n) {
    long i, j;
    long freq = n - 1;
    for (i = 2; i <= n; ++i) for (j = sqrt(i); j>1; --j) if (i%j == 0) { --freq; break; }
    return freq;
}

int main()
{
    std::cout << "Please wait for the result!" << std::endl;
    std::string word;
    std::ifstream data("Text.txt");
    while (data >> word)
        insert(word);
    long topCount = 0;
    for (long i = 0; i<10; i++)
        //cout << words[i] << " " << instances[i] << endl;
        std::cout << " File Name: " << word << "  Visitors #" << findTop(word) << std::endl;
    clock_t t;
    long f;
    t = clock();
    printf("Calculating...\n");
    f = frequency_of_primes(99999);
    printf("The number of primes lower than 100,000 is: %d\n", f);
    t = clock() - t;
    printf("It took me %d clicks (%f seconds).\n", t, ((float)t) / CLOCKS_PER_SEC);
    return 0;
}

Answer 1

函数get_file_name()在标题中找到第一个引号，在标题中找到最后一个引号，并进一步解析为文件名。这基本上就是@ AI.G。建议。但是，您可能希望了解C ++工具提供的正则表达式支持。

我也没有对输入或输出文件进行任何处理;这些信息刚刚被列为使用unordered_map的一个例子，如@PaulMcKenzie也建议的那样。

#include <iostream>
#include <fstream>
#include <unordered_map>

std::string get_file_name(const std::string& s) {
  std::size_t first = s.find_first_of("\"");
  std::size_t last = s.find_last_of("\"");

  std::string request = s.substr(first, first - last);

  std::size_t file_begin = request.find_first_of(' ');
  std::string truncated_request = request.substr(++file_begin);

  std::size_t file_end = truncated_request.find(' ');
  std::string file_name = truncated_request.substr(0, file_end);

  return file_name;
}


int main() {

  std::ifstream f_s("header_log.txt");
  std::string content;
  std::unordered_map<std::string, int> file_access_counts;

  while (std::getline(f_s, content)) {
    auto file_name = get_file_name(content);
    auto item = file_access_counts.find(file_name);

    if (item != file_access_counts.end()) {
      ++file_access_counts.at(file_name);
    } else {
      file_access_counts.insert(std::make_pair(file_name, 1));
    }
  }

  f_s.close();

  std::ofstream ofs;
  ofs.open ("output.txt", std::ofstream::out | std::ofstream::app);

  for (auto& n: file_access_counts)
    ofs << n.first << ", " << n.second << std::endl;

  ofs.close();

  return 0;
}