Ifstream is failing to load a file and it won't open - c++

Some of this code may seem foreign to you since I make 3ds homebrew programs for fun but it's essentially the same but with extra lines of code you can put in. I'm trying to read a file called about.txt in a separate folder. I made it work when I put it in the same folder but i lost that file and then my partner said he wanted it in Scratch3ds-master\assets\english\text and not in Scratch3ds-master\source I keep getting the error I coded in. I'm new to stack-overflow so this might be too much code but well here's the code:
#include <fstream>
#include <string>
#include <iostream>
int main()
{
// Initialize the services
gfxInitDefault();
consoleInit(GFX_TOP, NULL);
int version_major;
int version_minor;
int version_patch;
version_major = 0;
version_minor = 0;
version_patch = 2;
printf("This is the placeholder for Scratch3ds\n\n");
std::ifstream about_file;
about_file.open("../assets/english/text/about.txt");
if (about_file.fail())
{
std::cerr << "file has failed to load\n";
exit(1);
}

Chance are that you're using devkitpro packages. And chances are that the devkitpro team provide an equivalent of the NDS 'ARGV protocol' for 3DS programming. In which case, if you use
int main(int argc, char* argv[]);
you should have the full path to your executable in argv[0] if argc is non-zero.
https://devkitpro.org/wiki/Homebrew_Menu might help.
Your program has no a priori knowledge of what sort of arguments main() should receive, and in your question, you're using a main function that receives no argument at all.
Established standard for C/C++ programming is that main() will receive an array of constant C strings (typically named argv for arguments values) and the number of valid entries in that array (typically named argc for count). If you replace your original code with
#include <fstream>
#include <string>
#include <iostream>
int main(int argc, char* argv[])
{
// Initialize the services
// ... more code follows
then you're able to tell whether you received argument by testing argc > 0 and you'll be able to get these arguments values with argv[i].
With homebrew development, it is unlikely that you can pass arguments such as --force or --directory=/boot as on typical command-line tools, but there is one thing that is still useful: the very first entry in argv is supposed to be a full path for the running program. so you're welcome to try
std::cerr << ((argc > 0) ? argv[0] : "<no arguments>");
and see what you get.

Related

Using a program(.exe), inside a program, but passing command line arguments on linux C++

I've been trying to call a program inside another c++ program using the command "execvp()" from the <unistd.h> library but it gets core dump, and i dont know what i am doing wrong;
below its the code i use to call the program i want to use
#include <iostream>
#include <unistd.h>
int main(int argc, char **argv)
{
char *argument_list[]={argv[1],argv[2],NULL};
char *filename = "./bin/program.exe";
execvp(filename, argument_list);
return 0;
}
below this, its the code of the program i want to call
#include <iostream>
int main(int argc, char **argv)
{
int a = atoi(argv[1]);
int b = atoi(argv[2]);
std::cout << a+b<<std::endl;
return 0;
}
when i compile the the first code, i get a "main.exe" binary, then i type "main.exe 5 6" to sum both integers, and i get the "core dump" error.
Curious thing is, if i run gdb on it, i get the sum i want
the first command line, its running directly the "child" program, showing that it works. The second command line, its using the "main" program that calls the child one
(Obviously, this programs aren't the ones i need to apply this, they're just for illustration of the problem, they're really big codes, and it wouldn't be helpful to post them here);
How can i fix this?
So, it works if i set the first argument as the filename, as said by #WhozCraig, so now it works, and looks like this:
#include
#include <unistd.h>
int main(int argc, char **argv)
{
char *argument_list[]={"program.exe",argv[1],argv[2],NULL};
char *filename = "./bin/program.exe";
execvp(filename, argument_list);
return 0;
}
However, i get this warning:
1
How can i get around it? Is there a problem leaving it like this?

Fixing Segmentation Fault

I have to run this code for my class, most of what we use is java, I don't really know c++, but the code I have to run is c++, so I'm finding it difficult to debug or know what's going wrong. To compile it, I'm using a unix virtual machine. I've compiled it and have the a.out file in my directory. When I run the a.out file it says "segmentation fault". I've read that means it's trying to access something it can't, but I don't know what that would be. Is it a problem with the code they gave us, or could it be something like a setting on my machine?
#include <iostream>
#include <fstream>
#include <iterator>
#include <vector>
#include <algorithm>
#include <iostream>
#include <stdio.h>
using namespace std;
int main(int argc, char *argv[])
{
int N;
sscanf(argv[1], "%d", &N);
vector<double> data(N);
for(unsigned int i=0; i<N; i++) {
data[i] = rand()/(RAND_MAX+1.0);
}
sort(data.begin(), data.end());
copy(data.begin(), data.end(), ostream_iterator<double>(cout,"\n"));
}
This seems to be a matter of how you invoke the compiled binary. Say the executable is a.out, you should execute the program as
./a.out 42
as in this snippet
sscanf(argv[1], "%d", &N);
the size of the std::vector is parsed from the command line arguments. If you don't pass any arguments, argv has only one element (the executable name), and argv[1] is an out of bounds access, yielding undefined behavior. Note that you can use the argc variable to do some rudimentary error handling up front:
int N = 42; // some sensible default value
if (argc == 2)
sscanf(argv[1], "%d", &N);
This still won't protect you from trouble if the given argument is not parsable as an integer, but if you want to get into this, consider using a library for parsing command line options.

What's wrong with std::strings

Hi I am new to C++ and Code::Block
I am trying to make a simple code to test it, using strings.
when I compile the code there is no problem, but when I try to debug it, Code::Block gives me the following warning:
Cannot open file:
File:../../../../../src/gcc-4.9.2/libgcc/unwind-sjlj.c
Info: "Multiple information windows with the same message have been
supressed."
Image of the error FYI:
Part of the code that gives me an error.
inside main function
#include <iostream>
#include <string>
int main ()
{
std::mystring("What's wrong with strings");
return 0;
}
I realise that this error only occurs when I try to debug a string or a file containing a string.
Any help would be appreciated.
some other information that might help:
Code::Block 16.01
Compiler MinGW gcc4.9.2
Windows 7 Professional 32 bits SP1
First of all, to use strings you must include the file header string. And the name of the type string is..std::string, not std::mystring.
#include <string>
int main(int argc, char** argv)
{
std::string mystring("Nothing's wrong with strings");
return 0;
}
#include <iostream>
using namespace std;
int main ()
{
string mystring = "Whats wrong with my string";
return 0;
}
If you write it in the following way, it should work.
It's safer to define strings like I showed it. It will be also easier for you if you add using namespace std in the beginning of every program if you are new to C++.

Catch dynamically pass arguments to test cases

I have a C++ project which is being tested using Catch.cpp:
I compile and run the following file to run my tests:
#define CATCH_CONFIG_MAIN
#include "catch.hpp"
#include "test1.h"
#include "test2.h"
In the near future I'll want to run more complex tests, that require command line arguments.
In Other words, I would like to apply some logic to my tests runs, being able to run them from inside loops or conditions and pass variables to them.
I found this page: Supply your own main.
which seems like a good direction but i could not find a more detailed explanation.
Can this be done by catch? or maybe there is a better way to implement what i described?
What I managed to do is to write my own main, parse the command line and store the needed parameter (in my case an IP) in a global variable. Not the most beautiful code, but does the job:
#define CATCH_CONFIG_RUNNER
#include "catch.hpp"
std::string IP;
int main(int argc, char* const argv[])
{
Catch::Session session;
int returnCode = session.applyCommandLine(argc, argv, Catch::Session::OnUnusedOptions::Ignore);
if (returnCode != 0)
return returnCode;
for (auto token : session.unusedTokens()) {
printf("Token: %s\n", token.data.c_str());
IP = token.data;
}
return session.run();
}
I then run this as TestRunner.exe [test-case-tag] --MY_IP_HERE. Note that without the "--" in front of the parameter, they don't appear in the unusedTokens.

Windows std::ifstream::open() problem

I know there's been a handful of questions regarding std::ifstream::open(), but the answers didn't solve my problem. Most of them were specific to Win32, and I'm using SDL, not touching any OS-specific functionality (...that's not wrapped up into SDL).
The problem is: std::ifstream::open() doesn't seem to work anymore since I've switched from Dev-C++ to Code::Blocks (I've been using the same MinGW-GCC back-end with both), and from Windows XP to Vista. (It also works perfectly with OS X / xcode (GCC back-end).)
My project links against a static library which #includes <string>, <iostream>, <fstream> and <cassert>, then a call is made to functionality defined in the static library, which in turn calls std::ifstream::open() (this time, directly). Following this, the stream evaluates to false (with both the implicit bool conversion operator and the good() method).
Code:
#include "myStaticLibrary.hpp"
int main(int argc, char **argv)
{
std::string filename("D:/My projects/Test/test.cfg");
std::cout << "opening '" << filename << "'..." << std::endl;
bool success(false);
// call to functionality in the static library
{
std::ifstream infile(filename.c_str());
success = infile.good();
// ...
}
// success == false;
// ...
return 0;
}
stdcout.txt says:
opening 'D:/My projects/Test/test.cfg'...
When I open stdcout.txt, and copy-paste the path with the filename into Start menu / Run, the file is opened as should be (I'm not entirely sure how much of diagnostic value this is though; also, the address is converted to the following format: file:///D:/My%20projects/test/test.cfg).
I've also tried substituting '/'s with the double backslash escape sequence (again, slashes worked fine before), but the result was the same.
It is a debug version, but I'm using the whole, absolute path taken from main()'s argv[0].
Where am I going wrong and what do I need to do to fix it?
Please create a minimal set that recreates the problem. For example, in your code above there's parsing of argv and string concatentation, which do not seem like a necessary part of the question. A minimal set would help you (and us) see exactly what's going wrong, and not be distracted by questions like "what's GetPath()?".
Try to do this instead of assert(infile.good()):
assert(infile);
I have overseen the importance of the fact that the function in question has close()d the stream without checking if it is_open().
The fact that it will set the stream's fail_bit (causing it to evaluate to false) was entirely new to me (it's not that it's an excuse), and I still don't understand why did this code work before.
Anyway, the c++ reference is quite clear on it; the problem is now solved.
The following code:
#include <string>
#include <iostream>
#include <fstream>
#include <assert.h>
using namespace std;;
int main(int argc, char **argv)
{
std::string filename("D:/My projects/Test/test.cfg");
std::cout << "opening '" << filename << "'..." << std::endl;
std::ifstream infile(filename.c_str());
assert(infile.good()); // fails
return 0;
}
works fine on my Windows system using MinGW g++ 4.4.0, if I create the required directory structure. Does the file test.cfg actually exist? If you are opening a stream for input, it wioll fail if the file is not there.
Edit: To remove any DevC++ to CB issues:
build using command line only
make sure you rebuild the static library too