使用 C++ 替换文本文件中的单词

Question

I am looking for a way to replace a certain string (not an entire line) for my html file using C++. For example, if I have a html file that contains:

</span><br><span class=text>morning<br></span></td>

And I want it to edited as:

 </span><br><span class=text>night<br></span></td>

I need to replace "morning" by "night", and this is my code:

  string strReplace = "morning";
  string strNew = "night";
  ifstream filein("old_file.html");
  ofstream fileout("new_file.html");
  string strTemp;
  while(filein >> strTemp)
  {
    if(strTemp == strReplace){
       strTemp = strNew;
    }
    strTemp += "\n";
    fileout << strTemp;
   }

This code did not take any effect on my file, and I guess the reason is that it is only able to change the entire line, instead of partial string. Can someone give me some suggestions to do the correct implementation? Thank you in advance.

Answer 1

From how I read the original question, you need to replace all instances of "morning" in your file with "night", not just one instance on a given line. I would start by reading the entire file into a string.

std::string getfile(std::ifstream& is) {
  std::string contents;
  // Here is one way to read the whole file
  for (char ch; is.get(ch); contents.push_back(ch)) {}
  return contents;
}

Next, make a find_and_replace function:

void find_and_replace(std::string& file_contents, 
    const std::string& morn, const std::string& night) {
  // This searches the file for the first occurence of the morn string.
  auto pos = file_contents.find(morn);
  while (pos != std::string::npos) {
    file_contents.replace(pos, morn.length(), night);
    // Continue searching from here.
    pos = file_contents.find(morn, pos);
  }
}

Then in main,

std::string contents = getfile(filein);
find_and_replace(contents, "morning", "night");
fileout << contents;

EDIT: find_and_replace() should not declare its file_contents string parameter to be const . Just noticed and fixed that.

Answer 2

You can take the entire line, and then search and replace the substring. This way, you even skip the entire loop:

std::string line;

//Get line in 'filein'
std::getline(filein, line);

std::string replace = "morning";

//Find 'replace'
std::size_t pos = line.find(replace);

//If it found 'replace', replace it with "night"
if (pos != std::string::npos)
    line.replace(pos, replace.length(), "night");

Answer 3

There's multiple ways you can handle it. A pretty common one is making a file with the new strings in it, deleting the old file, and then renaming the new file to the old file name.

If that suits you, you can snag this console application.

---

Parameter 1 is the string to search for

Parameter 2 is the replacement text to use

Parameter 3 is the file path

---

Basically, I'm making some STD streams to the new file, and from the old file, locating the string in question if it exists, and if so, replace that string, and then pipe the result, regardless if substitution occurred as a new line for the new file.

Then, we're closing the streams, checking the file size, and if it succeeded to make a non-empty file, we're deleting the old file and renaming the new file to the old file name.

If the exit code aka errorlevel is 2, it means the input stream didn't work. If it's -1, that means we didn't successfully find and replace with a new file in-tact. If it's 1, that means you didn't provide the correct parameters. Only a zero exit will indicate success.

If you want to use this, you should add some exception handling, and probably a more robust file backup solution.

#include <iostream>
#include <fstream>
#include <string>
#include <sys\stat.h>

using namespace std;

int main(int argc, char * argv[])
{
    if (argc != 4) { return 1; }
    int exit_code = -1;

    string textToFind = string(argv[1]);
    string replacementText = string(argv[2]);
    string fileToParse = string(argv[3]);
    string fileToWrite = fileToParse+".rep";

    ifstream inputFileStream(fileToParse, ifstream::in);
    if (!inputFileStream.good()) { return 2; }

    ofstream outputFileStream(fileToWrite);

    string fileLine;
    while (getline(inputFileStream, fileLine))
    {
        size_t substringPos = fileLine.find(textToFind);
        if (substringPos != string::npos)
        {
            fileLine.replace(substringPos, textToFind.size(), replacementText);
        }       
        outputFileStream << fileLine << '\n';
    }
    outputFileStream.close();
    inputFileStream.close();

    struct stat st;
    stat(fileToWrite.c_str(), &st);
    int new_file_size = st.st_size;

    if (new_file_size > 0)
    {
        if (remove(fileToParse.c_str())==0)
        {
            if (rename(fileToWrite.c_str(), fileToParse.c_str())==0)
            {
                exit_code = 0;
            }
        }
    }

    return exit_code;
}