fstream write/read to a binary file doesn't work as expected.!

Question

#include <iostream>
#include <string.h>
#include <fstream>
#include <conio.h>
using namespace std;
int main(int argc, char*argv[])
  {
ifstream fpr;
ofstream fpw;

char * rec1 = "helloWorld";
char * rec2 = "my";
char out1[50];
char out2[50];
fpw.open("sample.txt",ios::in|ios::binary|ios::app);
if(fpw.fail())
{
    cout<<"The file could not be opened!\n";
    exit(1); // 0 – normal exit, non zero – some error
}
fpr.open("sample.txt",ios::out|ios::binary);
if(fpr.fail())
{
    cout<<"The file could not be opened!\n";
    exit(1); // 0 – normal exit, non zero – some error
}
fpw.write(rec1,10);
fpr.read(out1,10);
out1[10] = '\0';
cout<<out1<<"\n";
fpw.seekp(2,ios::beg);
fpw.write(rec2,2);
fpr.seekg(0,ios::beg);
fpr.read(out2,strlen(rec1));

cout<<"\n"<<out2<<"\n";
getch();
   }

With this code I just want to insert a string named 'my' to the 2byte location of 'helloworld' string. But it doesn't insert it(even though I'm seeking to the correct location). Could anyone help me out?

Answer 1

from documentation on ios::mode

ios::app:

the content to the current content of the file. This flag can only be used in streams open for output-only operations.All output operations are performed at the end of the file, appending

Remove the ios::app , and you will be able to write "my" over "ll" in `"helloworld".

Note that you won't be able to "insert" something into a file - the only way to achieve that is to read from the original file and write the new data to a new file [or read whatever is after you want to modify, insert the text you want, and write back the parts you want after the modified bit].