file writing

[bob]

Is there a way to overwrite a random byte in a file using FILE without
rewriting the whole file?

 

[Victor Bazarov]

Is there a way to overwrite a random byte in a file using FILE without
rewriting the whole file?

Yes. Open the file for reading/writing, then use fseek to get to the
position where you want to write, then use fwrite, then close it. IIRC
on some platforms you could end up with a truncated file unless you
open it for both reading and writing, you will need to check with your
documentation.

V

 

[Kern]

But it's quite classic way to moditfy the binary file.
How can we do this in a modern cpp way?

 

[bob]

is it fopen("file", "r+b");

???

 

[Tribal-Tec]

The modern cpp way would be the use of fstream;

std:fstream myFile; // or fstream for both writing and reading
myFile.open( "filename", std::ios_base::binary | std::ios_base:ut );

now with seekg method you can place the write cursor to modify your
desired byte.

Regards

 

[Chris Theis]

But it's quite classic way to moditfy the binary file.
How can we do this in a modern cpp way?

Surely you could use streams but what will you gain in this case?

Cheers
Chris

 

[BobR]

Tribal-Tec wrote in message

The modern cpp way would be the use of fstream;
std:fstream myFile; // or fstream for both writing and reading
myFile.open( "filename", std::ios_base::binary | std::ios_base:ut );

now with seekg method you can place the write cursor to modify your
desired byte.

The 'g' in 'seekg' means 'get' to me. Use 'seekp' to 'put'.

std:fstream MyFile("MyFile.txt", std::ios_base::binary );
if(!MyFile){ std::cout<<"\n ofstream FAILED"<<std::endl; /*exit(1);*/}
std::cout<<"ofstream MyFile.tellp() = "<<MyFile.tellp()<<std::endl;
MyFile.seekp(10, std::ios::end);
std::cout<<"MyFile.seekp(10, end) MyFile.tellp() ="
<<MyFile.tellp()<<std::endl;
MyFile.seekp(10, std::ios::beg);
std::cout<<"MyFile.seekp(10, beg) MyFile.tellp() ="
<<MyFile.tellp()<<std::endl;
MyFile.close();