Writing on last line with fstream

Question

I was trying to replace a string in a text file. Something like replace() function.

Here is the code:

#include <iostream>
#include <fstream>
#include <cstring>
Using namespace std;
int main()
{

fstream file("C:\\Users\\amir hossein\\Desktop\\Temp1\\test1.txt");

char *sub; sub = new char[20]; sub = "amir";
char *replace1; replace1 = new char[20]; replace1 = "reza";
char *buffer; buffer = new char[100];


int i, temp; streampos flag;
int c=0,mark;
bool flagforwrite=0;


if (file.is_open()){
    while (!file.eof()) {
        flag = file.tellg();
        file.getline(buffer, 100);    //We'll Search Sub inside of Buffer, if true, we'll replace it with Replace string
        flagforwrite=0;
        for (i=0;buffer[i];i++){
            mark=i; c=0;
            while (sub[c] && sub[c]== buffer[mark]){
                c++; mark++;
            }

            if (!sub[c]){   //Make Changes in The Line
                for (int j=i,count=0;count<strlen(replace1);j++,count++) buffer[j] = replace1[count]; //until here, we've replace1d the sub
                flagforwrite=1;
            }

        }

        if (flagforwrite){   //Write The line ( After Whole Changes In line have been made!!
                file.seekp(flag);
                file << buffer << "\n";   // ENDL here IS SUPER IMPORTANT!! IF you don't put it, I'll mess it up
                if(file.bad()) cout << "Error\n";
        }
    }
}

else cout << "Error!!\n";
file.close();  
delete[] sub;
delete[] replace1;
delete[] buffer;


return 0;
}

I want to replace "amir" with "reza".

My text file includes 4 lines:

Hi My name is amir and also my friend's name is amir too!
Hi My name is amir and also my friend's name is amir too!
Hi My name is amir and also my friend's name is amir too!
Hi My name is amir and also my friend's name is amir too!

When I run the program I get this.

Hi My name is reza and also my friend's name is reza too!
Hi My name is reza and also my friend's name is reza too!
Hi My name is reza and also my friend's name is reza too!
Hi My name is amir and also my friend's name is amir too!

What is wrong with the last line?

I think that problem is here:

if (flagforwrite){ 
                    file.seekp(flag);
                    file << buffer << "\n";
                    if(file.bad()) cout << "Error\n";
            }

Why is the flag always referring to the line?

I'm using GNU GCC compiler.

`file.seekp(flag);` You opened the file in text mode. Using functions such as `seekp` will not give you the desired results. http://stackoverflow.com/questions/33926595/text-file-binary-search If you want to process the file with any modicum of success, open the file in binary mode (`ios::binary`). — PaulMcKenzie, Feb 02 '16 at 23:03
Never do this: `while (!file.eof())`: https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong it often messes up the last line. — Galik, Feb 02 '16 at 23:56
Please write C++ code, instead of C code that uses C++. You're leaking memory, and you shouldn't even be allocating memory in the first place, rather using std::string, which supports all string operations that are manually implemented here. — Sam Varshavchik, Feb 03 '16 at 00:24

score 0 · Answer 1 · answered Feb 03 '16 at 09:14

0

I found the Problem! It was caused by eof()! so Instead of using while(!file.eof()) I used while(file.getline(buffer,100))

and I also Moved file.tellg() to the end, and defined line like this: streampos line=file.tellg();

answered Feb 03 '16 at 09:14

Amir Hossein

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Writing on last line with fstream

1 Answers1