Writing binary data to fstream in c++
Yes you can, this is what std::fstream::write
is for:
#include <iostream>
#include <fstream>
#include <cstdint>
int main() {
std::fstream file;
uint64_t myuint = 0xFFFF;
file.open("test.bin", std::ios::app | std::ios::binary);
file.write(reinterpret_cast<char*>(&myuint), sizeof(myuint)); // ideally, you should memcpy it to a char buffer.
}
Comments
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youR.Fate almost 2 years
Question
I have a few structures I want to write to a binary file. They consist of integers from cstdint, for example
uint64_t
. Is there a way to write those to a binary file that doesn not involve me manually splitting them into arrays ofchar
and using thefstream.write()
functions?What I've tried
My naive idea was that c++ would figure out that I have a file in binary mode and
<<
would write the integers to that binary file. So I tried this:#include <iostream> #include <fstream> #include <cstdint> using namespace std; int main() { fstream file; uint64_t myuint = 0xFFFF; file.open("test.bin", ios::app | ios::binary); file << myuint; file.close(); return 0; }
However, this wrote the string "65535" to the file.
Can I somehow tell the fstream to switch to binary mode, like how I can change the display format with
<< std::hex
?Failing all that above I'd need a function that turns arbitrary cstdint types into char arrays.
I'm not really concerned about endianness, as I'd use the same program to also read those (in a next step), so it would cancel out.
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youR.Fate about 6 yearsThat solves part of my problem. I'd like to be able to just use
<<
with my custom fstream. Can I somehow overload<<
for all (or a set of) cstdint types? Like a template that accepts a predefined list of types? -
YSC about 6 yearsYes, just define a new type using
std::fstream
in its implementation, with a templatedoperator<<
. -
youR.Fate about 6 yearsYes, but can I tell that template to only accept, for example uint64_t, uint16_t and uint8_t, but not for example, std::string, or bool?
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lmat - Reinstate Monica over 3 yearsYes. Yes you can.