Making a sequential list of files - c++

Question

I have been stuck on a problem for a while now and can't seem to find an answer.
I'm trying to create multiple files with the same name but a different number at the end each time, I have attempted this at first just by using
int seq_number = 1;
while (seq_number < 10)
{
ofstream fsave;
fsave.open("filename" + seq_number + ".txt");
fsave << "blablabla";
fsave.close();
seq_number = seq_number + 1;
}
But that gives me a very strange result where the letters get jumbled up, I'm not sure how that works but I know it doesn't.
I've looked online and found stringstream or sstream, and tried with that, but it keeps giving me errors too,
string filename;
filename = "character";
ostringstream s;
s << filename << seq_number;
filename(s.str());
fsave.open(filename + ".txt");
fsave << "blabla"
fsave.close(;)
but i keep getting an error:
no match for call to `(std::string) (std::basic_string, std::allocator >)'
I'm not sure how string stream works exactly so im working off of instinct, but i would appreciate any way this is possible, and honestly I think I would prefer doing it without sstream, but i need a way to get an int and str together and save a filename that is a string.
unless you know a better way ;) thanks guys

Answer 1

filename(s.str());
this is wrong; you are not constructing a new variable (filename is already constructed), what you want here is an assignment.
filename = s.str();
Then,
fsave.open((filename + ".txt").c_str());
(although, if you are using C++11, this change is not necessary)
Still, personally I would just construct the whole file name with the stream:
ostringstream s;
s<<"character"<<seq_number<<".txt";
fsave.open(s.str.c_str());
I'm not sure how string stream works exactly so im working off of instinct
This is a very bad idea, C++ is often quite a minefield of bizarre syntax, segfaults and undefined behavior, going by instinct usually leads to disaster.
About the errors you get:
fsave.open("filename" + seq_number + ".txt");
This shouldn't even compile, since you are summing an integer to a const char * (thus moving the "start of the string"), and then summing it again to a const char *, which is not allowed at all. Maybe it could compile if it were like this:
fsave.open("filename" + seq_number);
but it won't give the required result - "filename" is a pointer (not a C++ string), so summing an integer to it just moves the pointer of the given offset.
In your second snippet, instead, you are using an object (filename) as it were a function, which is only allowed if the class overloads operator(); thus, the compiler complains that such an operation is not allowed on that object.

Answer 2

Replace
fsave.open(filename + ".txt");
With
fsave.open( (filename + ".txt").c_str() );
This is because the ofstream constructor takes as parameter a char const *, not an std::string.
Also, your first version generates strange file names because in C and C++, adding an integer to a char * simply offsets within the character array. It does not append to the string.

Answer 3

In C++ you can not convert an int to a string, or concatenate it to one -- not to a ´char*`:
"filename" + seq_number + ".txt"
^const char* ^int ^const char*
Also, ostream can not recieve the filename as a string, it must be a const char*, which you can acquire temporarily via ´c_str()`.
Use sprintf, ostringstream (as you did), or C++11 to_string to do that:
#include <string>
#include <iostream>
int main() {
for(int seq_number = 1; i<10; ++i) {
std::string num_as_string = std::to_string(seq_number); // make a string, C++11
std::string filename = "abcd" + num_as_string + ".txt";
std::ostream f(filename.c_str());
f << "text\n";
}
}
This (modulo typos) should get you started.

Answer 4

You can do it like this:
ostringstream s;
s << "character" << seq_number << ".txt";
fsave.open(s.str());
fsave << "blabla";
fsave.close();
And this is how you could implement the original loop:
for (int seq_number = 1; seq_number<10; ++seq_number)
{
ostringstream s;
s << "filename" << seq_number << ".txt";
ofstream fsave(s.str());
fsave << "blablabla";
}

Answer 5

You could do something like this:
#include <iostream>
#include <string>
#include <sstream>
int main (int argc, char const* argv[])
{
std::string filename;
int seq_number = 10;
filename = "character";
std::stringstream s;
s << filename << seq_number << ".txt";
filename = s.str();
std::cout<< filename << std::endl; // <-- Here open your file instead print the filename
}