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File parse code to search and replace a string of text.

Posted on 2015-02-20
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Last Modified: 2015-02-21
I am looking for some C or C++ code that would parse a text file, and replace all occurrences of a string with another string.

So if I have a text file with this text : Mary had a little lamb who's name was Mary Anne.

And I want to replace "Mary" with "Terry",  how can I do that in C++. My file might have up to 1000 lines of text in it. The end result would be Terry had a little lamb who's name was Terry Anne.
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Question by:brgdotnet
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3 Comments
 
LVL 84

Accepted Solution

by:
ozo earned 250 total points
ID: 40622607
#include <iostream>
#include <string>
using namespace std;
string substitute(string str,string find,string replace){
  for( size_t i=0;(i = str.find(find,i))!=string::npos;i+=replace.length() ){
      str.replace(i,find.length(),replace);
  }
  return str;
}
int main ()
{
 string str;
 while( cin.good() ){
   getline(cin,str);
   cout << substitute(str,"Mary","Terry") << endl;
 }
 return 0;
}

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Assisted Solution

by:sarabande
sarabande earned 250 total points
ID: 40622875
the following program would read all text of a file to memory and replace Mary by Terry. finally the same file was written again.

#include <sys/stat.h>
#include <errno.h>
#include <fstream>
#include <string>

int main(int nargs, char * szargs[])
{
       struct stat fileinfo = { 0 };
       if (nargs < 2 || stat(szargs[1], &fileinfo) != 0) return -1;  // no commandline argument or file doesn't exist
       std::ifstream ifstext(szargs[1], std::ios::binary | std::ios::in);
       std::string buf(fileinfo.st_size, '\0');
       if (!ifstext.read(&buf[0], fileinfo.st_size)) return errno;
       ifstext.close();
       size_t pos, lpos = 0;
       while ((pos = buf.find("Mary", lpos)) != std::string::npos)
       {
              buf.replace(pos, sizeof("Mary")-1, "Terry");
              lpos = pos+1;
       }
       std::ofstream ofstext(szargs[1], std::ios::binary | std::ios::out);
       if (!ofstext.write(buf.c_str(), buf.length())) return errno;
       ofstext.close();
       return 0;
}

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you would call the program at the commmandline passing the filepath as argument.

note, the while loop is equivalent to the for loop ozo has used in the substitute function.

you may mix both codes by opening the file in text mode for read, then read line by line using std::getline from file, for each line do the substitution and add the modified line into a std::vector<std::string> container. finally close the file and open it again for write. write all the lines from vector back to the output file (note, you have to add a linefeed character to each line).

Sara
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LVL 84

Expert Comment

by:ozo
ID: 40623022
Note that the while loop would not be equivalent to the for loop if you wanted to replace "Mary" with "Mary, Mary, Quite Contrary"
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