How do I replace a string with another string? - c++

Question

I've sat on this problem for quite some time and I can't figure out, what to do.
I am trying to write a programm, that reads a text file, searches and replaces string and saves the file under a new name. Depending on your input with minimum and maximum value as well as inkrement, several files are created.
Everything works except the replacing of a string (function replaceVariable).
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <algorithm>
#include <conio.h>
using namespace std;
string replaceVariable(string text1, string oldVariable, long double wert){
cout<< "replace-function open............."<<endl;
size_t foundAt = text1.find(oldVariable); //find position of old variable
cout<<"position old variable: "<<foundAt<<endl;
string newText = to_string(wert); //convert long double 'wert' to string
cout<<"new variable: "<<newText<<endl;
size_t lengthNewText = newText.length(); //find length of new string
string text2= text1.replace(foundAt, lengthNewText, newText); //replace with new string with length 'lengthNewText' starting at position 'foundAt'
return text2;
}
void writeFile ( string text, string filename ){
ofstream myfile;
myfile.open ( filename.c_str() );
myfile << text;
cout<<"file written.............."<<endl;
myfile.close();
}
template <typename T>
std::string to_string(T const& value) {
stringstream sstr;
sstr << value;
return sstr.str();
}
int main(){
ifstream inFile;
inFile.open("C:\\Users\\User\\Desktop\\Test\\testing.txt");//open the input file
if (inFile.is_open()){
cout<< "file open"<<endl<<endl;
stringstream strStream;
strStream << inFile.rdbuf();
string str = strStream.str();
cout << "---------------------------------------------------------------"<<endl;
cout<< str << endl;
cout << "---------------------------------------------------------------"<<endl<<endl;
string line;
string name;
long double minWert = 0;
long double maxWert = 0;
long double inkWert = 0;
cout << "Enter minimum value:" << endl;
cin >> minWert;
cout << "Enter maximum value:" << endl;
cin >> maxWert;
cout << "Enter inkrement:" << endl;
cin >> inkWert;
int numFiles = (maxWert-minWert)/inkWert + 1; //calculation number of files needed
cout << "minimum value: " << minWert << endl;
cout << "maximum value: " << maxWert << endl;
cout << "inkrement: " << inkWert << endl;
cout << "number of files: " << numFiles << endl<<endl<<endl;
string oldVariable = "xyz "; //string to be replaced, xyz followed by 5 spaces
for( int fileNum = 1; fileNum <= numFiles; ++fileNum ) {
cout<< "loop number: "<< fileNum<<endl;
string output = str;
replaceVariable(output, oldVariable, minWert);
cout << "---------------------------------------------------------------"<<endl;
cout << output << endl;
cout << "---------------------------------------------------------------"<<endl<<endl;
string text = output;
name = "C:\\Users\\User\\Desktop\\Test\\comp";
name += to_string( fileNum );
name += ".bdf";
writeFile( text, name );
cout<<minWert<<endl;
minWert = minWert+inkWert;
cout <<"new Minimalwert: "<< minWert<<endl<<endl;
}
inFile.close();
} else{cout << "Unable to open file";}
getch();
return 0;
}
I've already searched numerous sites and googled every thinkable combination.
Do you have any ideas what might help?

Answer 1

If your functionality of the function 'replaceVariable' is right then this might be the issue,
string output = str;
/*function replaceVariable is returning replaced string but you didn't receive
at the calling place and assign back to output(which you are writing in output file)*/
replaceVariable(output, oldVariable, minWert);
So replace like,
string output = replaceVariable(str, oldVariable, minWert);

Answer 2

Several points to be noted in your code.
First, string::find may return npos if the pattern string is not found, you should check that.
Second, string::replace does an inplace replacement on the original string, for better performance you could pass the text1 argument by reference.
Third, replaceVariable only replaces the first occurrence of the variable, is that really what you want?
Here is my version of replacing patterns in a string:
// replaces at most `limit` occurrences of pattern `p` in text `s` with string `repl`.
// if `limit` <= 0, replace all occurrences.
// returns number of replacement that actually took place.
int replace(std::string &s, const std::string &p, const std::string &repl, int limit=0) {
int nrepl = 0;
size_t pos = 0,
plen = p.length(),
rlen = repl.length(),
npos = std::string::npos;
while ((pos = s.find(p, pos)) != npos) {
s.replace(pos, plen, repl);
pos += rlen;
++nrepl;
if (limit > 0 && nrepl >= limit) break;
}
return nrepl;
}
Hope that helps.