Member Avatar for skitzo315

I need some help with Binary I/O. I know how to do it when I am specifying the filename in the code
ie: fstream fio("persons.txt", ios::in | ios::out | ios::binary | ios::trunc); What I need to know is how to open or create a file with a file name that will vary and wont be persons. txt everytime. Basically, a file name specified by the user. How would I do that? I can't seem to find anything online for it. Also, please dumb it down for me, I'm still kind of new to this.

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  • Latest Post Latest Post by siddhant3s

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asked how to let the user pick a filename instead of hardcoding it. Early replies from , and pointed out the basic idea (use a variable; older compilers expect a C-style string). Below is a concise, practical pattern that handles filenames with spaces, creates the file if needed, and checks for open errors — using modern, safe idioms.

#include <iostream>
#include <fstream>
#include <string>

std::string filename;
std::getline(std::cin, filename);            // accepts spaces

std::fstream fio;
fio.open(filename, std::ios::binary | std::ios::in | std::ios::out);

if (!fio.is_open()) {                        // create if it didn't exist
    std::ofstream create(filename, std::ios::binary);
    create.close();
    fio.open(filename, std::ios::binary | std::ios::in | std::ios::out);
}

if (!fio) {
    std::cerr << "Unable to open file: " << filename << '\n';
    // handle error (permissions, invalid path, etc.)
}

Notes and troubleshooting tips: operator>> stops at whitespace, so prefer std::getline for filenames with spaces. Including std::ios::out (or using std::ofstream) creates the file; std::ios::trunc will erase contents; std::ios::app appends. Always test .is_open() or .fail(), or set exception masks with .exceptions(...) for stricter error handling. For portability and Unicode paths prefer std::filesystem::path (C++17+).

Cautions for binary I/O: avoid writing raw in-memory structs directly (padding and endianness cause portability problems). Use explicit serialization (defined byte layout or a binary format) for stable storage. Also validate/sanitize user-supplied paths and check directory existence and permissions before opening.

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Member Avatar for death_oclock

Replace "persons.txt" with a string variable containing the filename you have gotten from the user. I hope you know how to get user input...

By the way, code tags should look like this:
&#91;code=c++&#93; ...your code... &#91;/code&#93;
The fact that you tried is appreciated, however :P

Member Avatar for daviddoria

You will need to use the c_str() function of the string because a lot of these function accept an array of characters, not an actual string.

#include <string>
using namespace std;

string filename = "whatever.txt";
fstream fio(filename.c_str(), ios::in | ios::out | ios::binary | ios::trunc);

Dave

Member Avatar for siddhant3s

If you are using C++ <string>

string s1;
cin>>s1;
fstream fio(s1.c_str(), ios::in | ios::out | ios::binary | ios::trunc);

But if you are using an old compiler, Like Turbo C++(although, I recommend you to switch to a new compiler, Read the Article :http://cppdb.blogspot.com/2008/10/why-you-shouldnt-use-you-use-old-c.html)

char s1[50];
cin>>s1;
fstream fio(s1, ios::in | ios::out | ios::binary | ios::trunc);

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