my c++ file is not opened , why? - c++

Question

cout<<"enter name of file : " <<endl;
char nof[30] ;
for (int i=0;i<20;++i){
cin>>nof[i];
if (nof[i-1]=='x'){
if (nof[i]=='t'){
break;
}
}
}
fstream file1;
file1.open(nof);
if (file1.is_open()) cout<<"file is open"<<endl;
that is a code which should take the name of file from user to create
but i checked if it is opened and it is not , what to do ?

Answer 1

Try using this:
#include <string>
#include <iostream>
#include <errno.h>
#include <fstream>
#include <cstring>
using namespace std;
int main() {
cout << "Enter the name of the file : ";
string file_name;
getline(cin, file_name);
fstream file_stream;
file_stream.open(file_name);
if (file_stream.is_open()) {
// File Stuffs goes here...........
cout << "The file is open" << endl;
} else {
// The file may not exists or locked by some other process.
cout << strerror(errno) << endl; // Edited this line.
}
}

Answer 2

The way you handle user input make variable nof a invalid file path on your running os. That's why fstream::is_open() return false.
for (int i=0;i<20; ++i){
cin >> nof[i];
if (nof[i-1]=='x'){
if (nof[i]=='t'){
break;
}
}
}
This code takes user input until it gets xt. But in C/C++, a valid string of char* or char[] type has to be end with \0 character. So if you still love the way you handling input, append \0 to the end of nof before you break the loops.
for (int i=0;i<20; ++i){
cin>>nof[i];
if (nof[i-1]=='x'){
if (nof[i]=='t'){
nof[i+1]=0; //or nof[i+1]='\0' or nof[i+1]=NULL;
break;
}
}
}
But I suggest you use std::string and getline instead, the above way is quite awkward.
std::string nof;
std::getline(std::cin, nof);
std::fstream file;
file.open(nof.c_str(), std::fstream::in | std::fstream::out);

Answer 3

Mohit's answer tells you how to detect failure of std::fstream::open.
That function would usually use some operating system service to open a file, generally some open system call like open(2) on Linux (which can fail for many reasons).
Your program is buggy because your nof probably does not contain a valid file path. I would recommend clearing it with memset(nof, 0, sizeof(nof)) before reading it, and using your debugger, e.g. gdb to find your bug (if you enter a filename of only three characters, or one of fourty letters, your program won't work)
You could ask your operating system for a reason of that failure. On Linux you would use errno(3) (e.g. thru perror(3)).
As far as I know, the C++ standard does not specify how to query the reason of the failure of std::fstream::open (and probably do not require a relation between fstream and errno)
Pedantically, the C++ standard does not require std::fstream to use operating system files. Of course, in practice, fstream-s always use them. But in principle you might have a C++14 implementation on something without files or even without an OS (but I cannot name any).
The notion of file is in practice tightly related to operating systems and file systems. You can have OSes without files (in the past, OS/400, PalmOS, GrassHopper and other academic OSes) even if that is highly unusual today.
And the notion of file is specific to an OS: A file on Windows is not the same as a file on Unix or on z/OS.
Languages standard specifications (like C++11 n3337, C11 n1570, Scheme R5RS) are written in English and they are purposely vague on "files" or "file streams" (precisely because different OSes have different notions of them).