Alright, so I could have sworn this worked in my program earlier, but now I'm being driven mad by std::fstream. I just want to open a file from command line arguments, ie.
./main Program1.S
should open the file Program1.S and scan it.
Here is how I set up a open_file() function in my code:
#include <string>
#include <iostream>
#include <fstream>
void open_file(std::fstream &ifp, std::string file_name) {
ifp.open(file_name, std::ios::in | std::ios::out);
if(ifp.fail()) {
std::cout << "File not found." << std::endl;
exit(1);
}
}
void close_file(std::fstream &ofp) {
if(ofp.is_open()) {
ofp.close();
return;
}
std::cout << "This file is not currently open" << std::endl;
}
int main(int argc, char * argv[]) {
std::string in_name;
in_name = argv[1];
std::fstream ifp;
open_file(ifp, in_name);
// do some processing
close_file(ifp);
return 0;
}
Now, I compile my program using (unfortunately I am required to use c++03): g++ -g -std=c++03 -Wall -pedantic main.cpp -o main
Compilation works and provides no errors, but when running the program using: ./main Program1.S, it goes to File not found in open_file(). I even checked what was in argv[1] and it is definitely a file that is in the current working directory. Is there something wrong with the way I am doing this?
Check to make sure your file has been added to your project folder. Otherwise, you need to specify a file path within your computer ex. "/Mac HD/Documents/myfile". The program has no idea what to do with a external file name without its file path. Hope this helps.
Related
I have some trouble with producing files in C++. I consulted this answer here but when I try using it, it doesn't produce a file. What I wrote:
//~/Documents/Test_CPP/ex2/main_2.cpp
#include <fstream>
int main()
{
std::ofstream file("Hello.txt");
// Hello.txt has been created here
}
I compile it with the command g++ main_2.cpp and run it with ./a.out. I don't really know what could go wrong here, except theorizing that the file might be produced not in the current directory but somewhere else. So I tried changing Hello.txt to ~/Documents/Test_CPP/ex2/Hello.txt, which doesn't change anything. What exactly am I doing wrong here?
I have encountered this problem on macOS with Xcode if you use some IDEs you should point to build-dir.
My suggestion: use std::filesystem::current_path(). It will give full path to you elf\exe dir.
#include <string>
#include <iostream>
#include <filesystem>
#include <fstream>
int main() {
std::string file_name{"Hello.txt"};
auto path{std::filesystem::current_path()};
path = path / file_name;
if (std::filesystem::exists(path)) {
std::filesystem::remove(path);
}
std::ofstream out_stream(path, std::ios::out);
if (!out_stream.is_open()) {
std::cerr << "Error open file" << std::endl;
return -1;
}
out_stream << "test" << std::endl;
out_stream.close();
return 0;
}
This can sometimes happen if you do not properly terminate the connection to the file
EG.
file.close();
This must be done before the program terminates.
I am trying to open a text file, and the code below is my attempt:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main() {
std::ifstream file;
file.open("InputFile.txt");
std::string fileOutput;
if (file.is_open())
{
while (!file.eof())
{
file >> fileOutput;
std::cout << fileOutput << std::endl;
}
}
else
{
std::cout << "File failed to open" << std::endl;
}
file.close();
return 0;
}
The text file is located on my desktop, and it only contain two integers.
Whenever I run the code above, it will show me the "file failed to open" message. I am completely new to c++, so I really don’t have any idea why my code is not working. So any comments would be appreciated.
The text file is located on my desktop
So where is your C++ source file, is it located in my desktop as well?
Note this code file.open("InputFile.txt"); tries to open the InputFile.txt in the current folder, that means it only works if both C++ source file and your text file are in the same folder. That seems to be your problem.
Like #ShadowRanger's this comment, the existing answers are both inaccurate. The argument for file.open() needs to either 1. reflect the relative location of the text file in relation to the current working directory (where you are calling the executable from), or 2. give the absolute location of the text file on the disc.
I suggest the following solution:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(int argc, char** argv) {
if (argc != 2) {
std::cout << "incorrect number of inputs" << "\n";
std::cout << "correct usage: this_executable.exe file_location" << "\n";
return -1;
}
std::ifstream file;
file.open(argv[1]);
std::string fileOutput;
if (file.is_open())
{
while (file >> fileOutput)
{
std::cout << fileOutput << std::endl;
}
}
else
{
std::cout << "File "<< argv[1] <<" failed to open" << std::endl;
}
file.close();
return 0;
}
This solution takes the file's address info out of the code. With this solution, when you call your executable, the file's address(directory path + file name) is given to the executable at run-time rather than compile-time. Now, you'd run the executable like:
C:\path_to_your_exe>my_executable.exe C:\path_of_your_txt_file\InputFile.txt
The benefits of this approach are:
You can change the file's name / path without having to recompile the code;
On the commandline, it is easier to check that the target file's address is correct by tab completion
Also note:
As #ShadowRanger also pointed out the Why is “while ( !feof (file) )” always wrong? issue which I was not aware of.
If you are wondering what argv[1] means, see this guide for more information on commandline arguments for C++. You also want to make sure to catch situations when the user did not specify an input (meaning argv[1] is invalid, thus the argc != 2)
Unless the file you are opening and your executable are in the same directory, the same message will be printed since it will search for the file in the current working directory. You can specify the absolute path to the file on your desktop using %USERPROFILE%\\Desktop\\InputFile.txt or any other environmental variable that maps the absolute path of a disk, from which your file can be found.
I have a hello.cpp file:
#include <fstream>
#include <iostream>
using namespace std;
int main()
{
cout << "hello" << endl;
ofstream file;
file.open("codebind.txt");
file << "this text is written using C++\n" << "This is a number: " << 10;
file.close();
return 0;
}
After compiling this file by g++ using command prompt: g++ -o output hello.cpp, it generated a output.exe file. Then, I managed to run this output.exe file in another .cpp program called program.cppusing CreateProcess() (link for code). Unfortunately, when I hit Build, the system did not create any codebind.txt file despite the fact that the exitcode variable in program.cpp had a value of 0 as expected. Then I tried going to Explorer and running hello.exe mannually, it created the codebind.txt file.
Could someone tell me what's wrong with my program.cpp file and how to create codebind.txt using CreateProcess? Any help will be appreciated!
I have this short program:
#include <cstdlib>
#include <iostream>
#include <fstream>
#include <string>
int main (int argc, char * argv[]) {
std::string homedir = std::getenv("HOME");
std::string filename = argc > 1 ? argv[1] : (homedir + "/" + "file");
std::cout << homedir << std::endl;
std::cout << filename << std::endl;
std::fstream file;
file.open(filename, std::ios::out);
file << "Yo yo waddup" << std::endl;
file.close();
return 0;
}
When I supply no arguments, it opens a file in the users home directory. That of course makes sense. But when I run it from a different directory like this:
$ ./folder/hometest examplefile
The program creates "examplefile" in my current directory instead of the directory where the program is.
Why exactly is this happening?
Why exactly is this happening?
The program is behaving just as expected.
The file is opened relative to the current work directory, not where the executable is located.
If it didn't work that way,
All your programs will have to work with absolute paths, or
The location of the program will be flooded with files. First, that might not be possible because of permissions issue. Second, in a multi-user system, users will end up trying to create the same file names/directories.
Neither of the above is desirable.
Hi I am trying to read a Wavefront file which was created using Blender. I put a copy of this file into the solution Explorer. When I tried to compile for the first time I got the following message:
fatal error LNK1107: invalid or corrupt file: cannot read at 0x...
It seemed like the compiler confused Blender's .obj files with some other format which also uses the .obj ending. The solution was to exclude the file from the build process in its properties.
Now the application does compile but there is no data displayed like I would expect it. Not sure if this is a code issue.
#include "stdafx.h"
#include <iostream>
#include <stdlib.h>
#include <fstream>
#include <string>
using namespace std;
void ReadPrintFile(string _fileName)
{
std::string line;
std::ifstream fileStream (_fileName);
if (fileStream.is_open())
{
while (getline(fileStream,line))
{
cout << line << '\n';
}
fileStream.close();
}
else
{
cout << "Unable to read file";
}
}
int _tmain(int argc, _TCHAR* argv[])
{
ReadPrintFile("Drone.obj");
std::cin.get();
return 0;
}
The code does not jump into the else statement. The filestream simply seems to be empty and I am directly forwarded to the cin.get(); statement. I know that there are tons of tutorials on how to parse .OBJ in C++ but I want to understand.
The trick was not to copy the file into the solution explorer but into the project folder.