I am relatively new to using the boost library for c++ and I am wondering how to open a file using this. My aim is to read from a json file however I do not know how to open the file.
In c++, you can do this
int main () {
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
}
but how can I do this using boost?
You can use boost::filesystem::ifstream (which works with a boost::filesystem::path instance) or simply use a std::ifstream to read the file.
The actual code depends a lot on your concrete use-case.
Related
I want to print some data to a file with a few separate calls. I noticed that the default behaviour for a write overwrites the previously written data.
#include <iostream>
#include <fstream>
using namespace std;
void hehehaha (){
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
}
int main () {
for(int i=0; i <3 ; i++){
hehehaha();}
return 0;
}
this code writes only one line Writing this to a file. but what I want is the following:
Writing this to a file.
Writing this to a file.
Writing this to a file.
Open the file in app mode instead myfile.open("example.txt", std::ios_base::app);
The default open mode for ofstream is plain out, which recreates the file from scratch (if the file exists, its contents is truncated).
To append to a file you need to use the app mode, or add the flag ate.
The table in this open reference is quite helpful to understand the open-modes and what they do.
I want to print some data to a file with a few separate calls. I noticed that the default behaviour for a write overwrites the previously written data.
#include <iostream>
#include <fstream>
using namespace std;
void hehehaha (){
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
}
int main () {
for(int i=0; i <3 ; i++){
hehehaha();}
return 0;
}
this code writes only one line Writing this to a file. but what I want is the following:
Writing this to a file.
Writing this to a file.
Writing this to a file.
Open the file in app mode instead myfile.open("example.txt", std::ios_base::app);
The default open mode for ofstream is plain out, which recreates the file from scratch (if the file exists, its contents is truncated).
To append to a file you need to use the app mode, or add the flag ate.
The table in this open reference is quite helpful to understand the open-modes and what they do.
ifstream myfile;
myfile.open("FileTest");
string line;
if(myfile.is_open())
{
cout<<"Reading from file...";
getline(myfile,line);
}
if(myfile.fail())
{
cout<<"Unable to open file"<<endl;
}
myfile.close();
C++ tries to open the file in the current directory with the exact name FileTest. Check to see if the file is in the current directory? Maybe you spelled the name incorrectly? Maybe you forgot to write FileTest.txt? You are using ifstream, which will fail if the file you're trying to open does not exist or is corrupted.
I want to create thousands of file with txt extension in c++. Is it possible? I can not imagine how can i do that. If I write some code right here so you can understand what I want.
int main ()
{
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
}
I want to generate a bulk of txt of files with this method. In addition I want to run these codes inside a for structure. At the end of the operation I must have 10,000 file and these file's names are like example1.txt , example2.txt , example3.txt ... You do not have to write code I just want to know how to do it. You can just share link to some tutorial.
Yes, you can do that. Here are the steps I suggest:
Use a for or a while loop.
In each iteration of the loop construct the name of a unique file by using the loop counter. You can use std::ostringstream or sprintf for that.
Use the code you already have to create a file in each iteration of the loop.
#include <fstream>
#include <iostream>
int main () {
std::ofstream myfile;
for(int i=1;i<=1000;i++){
myfile.open("example" + std::to_string(i) + ".txt");
myfile << "Writing this to a file.\n";
myfile.close();
}
return 0;
}
I've been trying to learn File IO in C++ via tutorial webs and came across the following code.
Now, how do I specify the location of the output file? I've tried running the code and search for the location of the file but didn't work.
Thank you.
ofstream myfile ("InOutExample.txt");
if (myfile.is_open())
{
myfile << "This is a line.\n";
myfile << "This is another line.\n";
myfile.close();
}
else cout << "Unable to open file";
return 0;
system("pause");
If you specify the location, it will put it there.
ofstream myfile ("c:\\temp\\InOutExample.txt");
If you don't put a full path, it puts it in the current working directory.