C++ program to find and replace a string in file

Question

This is a beginner question. I am trying to find a string in text file and replace it back to the same file. Following code works fine collecting contents of file into buffer and replace the string . But when i try to keep the data back to same file, it is filled with some junk character. Please let me know what I am doing wrong ?

#include <iostream> #include <fstream> using namespace std; const char *fileName = "Test.dat"; int main () { // This is where we'll put the stuff we read from file char buffer[ 100 ]; ifstream finout(fileName, ios_base::in | ios_base::out | ios_base::binary); if(!finout.is_open()) { cout << "Can not open file " << endl; return(1); } while (finout.getline(buffer, sizeof(buffer)) { string g( buffer ); string search = "am"; string replace = "was"; long j; if ( (j = g.find(str2)) != string::npos) { g.replace(g.find(str2), str2.length(), "str"); finout.write((char *) &g, sizeof(g)); //This won't work } cout << g << "\n"; finout.close(); return 0; }

My Test.dat file contain following information:

Hello, How are you? I am fine.

masoud · Accepted Answer · 2013-03-11 06:55:03Z

1

When you are read/write as a text file, do not open it by ios_base::binary
You put finout.close(); inside your reading loop, so it just work for one line.
When you are reading/writing a file as a text, use text stream methods and operators.

answered Mar 11, 2013 at 6:55

masoud

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user1768029 Over a year ago

Thanks !! It worked. I wrote altered contents into a temporary file. And added following code to copy the temp file contents to original after while loop. finout << fout.rdbuf; if(!fout.eof()) std::cerr << "reading from file failed\n"; if(!finout.good()) std::cerr << "writing to file failed\n"; now fout points to temp file. But everytime it throws error that reading from a file is failed. Did i miss anything here ?

EGOrecords · Accepted Answer · 2013-03-11 06:57:32Z

You are trying to read the size of your string with the sizeof() operator.

This wont work, because it is a keyword, that gives you the non-dynamic size of the object or type.

You should use g.size() to access the string size!

But on the first place, you can handle the stream handle your bug:

finout << g;

will do the job.

Elvis Teixeira · Accepted Answer · 2014-09-10 11:15:51Z

First, you want to both read and write a file, so use fstream not ifstream. Second, you have a text file, so don't use ios_base::binary Third (char*) &g where g is std::string doesn't work, use g.c_str() instead. (simply write finout << g;

Now you can start thinking of the implmentation...

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