Thread: Ask me about C / C++

I have a console application using a case block to open some files. I just need the syntax for an 'open file' command.

Can I ask, is this only with C++ or other C languages too?

EDIT-
Also, do compiled C++ programs have to run on an IDENTICAL system? (Same operating system, same CPU etc) I read this in an e-book once and switched back to Visual Basic.

Originally Posted by The Invisible Man

I have a console application using a case block to open some files. I just need the syntax for an 'open file' command.

Ugh, files are a pain. There are good libraries out there (I use wxWidgets,) but pure C is hard.

Code:

FILE* file = fopen("yourfile", "w");  //w for write, r for read, a for append
if(file!=NULL){
  /*
    fwrite and fread are what you need
    fwrite(buffer, size of element, number of elements, file pointer)
  */
  size_t check =  fwrite("Stuff to write", sizeof(char), 14, file);
  if (check != 14) printf("Writing failed");
}
fclose(file)

Originally Posted by Dairyman

Can I ask, is this only with C++ or other C languages too?

I only know C and C++, I don't know C# or objective C.

Also, do compiled C++ programs have to run on an IDENTICAL system? (Same operating system, same CPU etc) I read this in an e-book once and switched back to Visual Basic.

Yes, that's no different than any other programming language that does native compiling. A program written in C++ or C compiled on OSX will only run on OSX, Windows programs will only run on Windows. CPU doesn't matter... mostly (AMD=AMD64=Intel=Intel64!=PPC)

It's very easy to fix though, a few preprocessor commands will allow you to compile on any system.

Crap, I meant C++. Sorry, but... um.... yeeeeeeeeeeeeaaaaaaaaaaah. Could I get that the Open File command on C++? Command for the Standard Library?

Yes, but it's in a different library in C++, I think it's in <iostream>

I have <iostream> and <stdlib.h>. What's the command?

They are the same as C. C++ is a [nearly] complete superset of C.

What language did you learn before C & C++?

Basic and assembly.

So you're saying

Code:

#include <iostream>
#include <stdlib.h>
int main()
{
FILE* file = fopen("yourfile", "w");  //w for write, r for read, a for append
if(file!=NULL){
  /*
    fwrite and fread are what you need
    fwrite(buffer, size of element, number of elements, file pointer)
  */
  size_t check =  fwrite("Stuff to write", sizeof(char), 14, file);
  if (check != 14) printf("Writing failed");
    fclose(file)
                  }
}

This is what I type into my IDE to open the file/app/.exe?

Sorry to bug you like this, but I'm not sure if you were answering my question.

Yes, that's how you open a file, write the words "Stuff to write" to it, and then close it again.

You can do file i/o the fstream way too, which is usually cleaner.

let's just say this. it's "has an ass rocket, kills self, and goes to hell" (AKA Infinity) hard.

68000 ASM is probably easier.

An idea I just had regarding ebooks and the library system led me here...

Say a library wanted to set up a proprietary program and ebook format to offer ebooks from their website that could be downloaded, but would 'expire' in a set period—say 30 days. This way they could offer the same selection for download as they did at the physical location, but on the same principle. Would C or C++ be the preferred method of designing said program, or would another method be better? At the simplest level, what would be involved in something like this?

Just a thought I had, while I was wishing I could just download any book I wanted to read—legally.

*cough* warez-bb *cough*

Originally Posted by The Invisible Man

Crap, I meant C++. Sorry, but... um.... yeeeeeeeeeeeeaaaaaaaaaaah. Could I get that the Open File command on C++? Command for the Standard Library?

Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main(){
    fstream FILE("foo.txt",ios_base::trunc); //First, we open a file named "foo.txt", overwriting any existing data. (signified by ios_base::trunc for truncate ;))
    
    if(!FILE.is_open();){ //If the file opens, then continue
        FILE<<"Stuff to write\n"; //Write to the File stream using the insertion operators <<
        string In;
        FILE>>In; //Read from the stream using the extraction operators >>
    }
    return EXIT_SUCCESS; //Because macros are just way cooler than constants
}

Originally Posted by Man of Steel

An idea I just had regarding ebooks and the library system led me here...

Say a library wanted to set up a proprietary program and ebook format to offer ebooks from their website that could be downloaded, but would 'expire' in a set period—say 30 days. This way they could offer the same selection for download as they did at the physical location, but on the same principle. Would C or C++ be the preferred method of designing said program, or would another method be better? At the simplest level, what would be involved in something like this?

Just a thought I had, while I was wishing I could just download any book I wanted to read—legally.

Better reduce the "loan time" on those
anymore than 48 hours and you risk having your "restriction" cracked

Something like an expiring book just wouldn't work....
I know you know better than this,
but anyhow

Step though the program with a "legitimate" book
Step though the program with an "expired" book
find the fork
redirect the expired fork down the legitimate fork

In all honesty, kids stuff

As a book publisher, you have just spent god-knows how much money buying this DRM mechanism from someone, and it's cracked in hours

About the only way to realistically overcome this, is to require authorisation over the internet each time you open an e-book
which would be crap, and only annoy people

The "loaning" of things is a mechanism devised in the physical world of scarce products that cost money to reproduce
It doesn't translate (sanely) over into the digital world

Originally Posted by Ynot

Better reduce the "loan time" on those
anymore than 48 hours and you risk having your "restriction" cracked

Something like an expiring book just wouldn't work....
I know you know better than this,
but anyhow

Step though the program with a "legitimate" book
Step though the program with an "expired" book
find the fork
redirect the expired fork down the legitimate fork

In all honesty, kids stuff

As a book publisher, you have just spent god-knows how much money buying this DRM mechanism from someone, and it's cracked in hours

About the only way to realistically overcome this, is to require authorisation over the internet each time you open an e-book
which would be crap, and only annoy people

The "loaning" of things is a mechanism devised in the physical world of scarce products that cost money to reproduce
It doesn't translate (sanely) over into the digital world

Aye, I agree/know that, realistically speaking, it would never work. Just wishful thinking, really, and thought it posed an interesting hypothetical question for this thread. I guess the more practical way to do something of that nature would be via the internet, using Flash to prevent easy copy & pasting. Even that would be less than ideal, of course.

*sigh*

Yes, C++ is the most powerful language that there is, you can use it for something like that. However, I wouldn't use a timestamp, seeing as people can change their system time. I remember Apple having a problem with people renting movies on iTunes and then setting back their clocks.

Hey, I am trying to cover the basics of C++.
I think I have some of them down, I just need to double check if I'm right.

Code:

#include "stdafx.h"
#include <iostream>

using namespace std;

int main()
{
    cout << "Here is some text";
    cout << endl;

    cout << "What is 15 + 17? the answer is:";
    cout << 15 + 17;

    cin.get();
    return 0;
}

Above is the first code I have written for C++, I found a little beginners tutorial for it. It is important to understand the code, so here it goes.

Code:

#include "stdafx.h"
#include <iostream>

They tell the compiler to include these in the .exe
They are both separate files containing code.
stdafx.h is a header code and isostream contains different packages that do several things.

Code:

using namespace std;

Tells the computer that it wants to use the package 'std' from ;isostream

Code:

int main()

Is the main function which every piece of code should have.

Code:

{

Opens the code.

Code:

cout << "Here is some text";

'cout <<' gives the program a output, or something to print. In this case its a line of text.
Cout is a keyword taken from the package 'std' which is in 'iostream;

Code:

cout << endl;

'endl' ends the line

Code:

cout << 15 + 17;

This tells the computer to print the answer of this calculation.

Code:

cin.get();

This makes the program wait for an input by the user

Code:

return 0;

Once it has the input, it tells the computer to revert back to what it was doing before hand

Code:

}

closes code




I was wondering if you could check if I have it all right.
If there's anything I am missing as a beginner.. I would appreciate it if you point it out


thanks

Originally Posted by A Roxxor

Code:

using namespace std;

Originally Posted by mrdeano

Code:

#include "stdafx.h"
#include <iostream>

They tell the compiler to include these in the .exe
They are both separate files containing code.
stdafx.h is a header code and isostream contains different packages that do several things.

Yes.

Code:

using namespace std;

Tells the computer that it wants to use the package 'std' from ;isostream

... kind of... That tells it to use the std namespace throughout the program. It is considered better programming technique to only have a namespace over small scopes. It actually allows you to transcend scope, this is very useful in large programs so that you don't have duplicate variables and have to worry about concurrency.

Code:

int main()

Is the main function which every piece of code should have.

Yes, it's the entry point of the operating system, there is more to it, but you don't need to know that unless you are doing assembly optimizations.

Code:

cout << "Here is some text";

'cout <<' gives the program a output, or something to print. In this case its a line of text.
Cout is a keyword taken from the package 'std' which is in 'iostream;

Code:

cout << endl;

'endl' ends the line

Yes, cout is a stream that goes to the terminal, the real thing that you need to take away from that line is the << operator. There are lots of functions that use it, you can create classes and use STL libraries to send strings through pipes, files, even the internet.

endl is a std const for cross compatibility, most programers use \n instead though, even though we shouldn't

Code:

cin.get();

This makes the program wait for an input by the user

Yes, more specifically keyboard input, inputs from other devices won't trigger this method.

Code:

return 0;

Once it has the input, it tells the computer to revert back to what it was doing before hand

Kind of, it tells the operating system to close the program and return an error code of 0. Returning things other than zero from the main loop tells the operating system that something went wrong, and depending on the code and the OS, it may attempt some type of recovery. From -127 to -1, the system may try a recovery, from 1 to 127, it is a user-defined error and will not produce any type of recovery on the OS level, it may be read by a calling or forking program though.

I have a package called "atomic parsley". Instead of a make file, it has a shell script with commands to compile each unit without linking, then goes through a second time and links everything. Each source file seems to have all the includes it needs, as-is. But on the compile w/o linking stage, it's using g++ with command line options which I don't know the importance of, which fail with a syntax error on all the c compilers I've got, even the version of gcc I have.

Are there any quick guides to creating a proper make file for projects lacking one?

Ouch, creating makefiles for large projects suck

What options are being set that you don't know the significance of? Most likely the problem is that the program was written in Visual C++ and not GNU C++. M$ doesn't adhere to C++ standards, so their software won't work in other compilers, that's why so few people write in Visual C++ outside of M$ itself.

The basic makeup of a makefile is setting the flags to variables, the creating a command for each file. Here's a good tutorial.

What options were being set that you didnt' understand?

The most common ones are:
-c : compile, but don't link
-O1, O2, O3, Os : optimization levels
-strip : strip unnecessary symbols and code
-o : send to this output file
-l : link a library
-I : include paths
-g : include debugging information it the executable
-Wall : Warnings All - warns you about everything

Yes, I've been figuring that this will suck. But I really need some kind of code for dumping itunes m4a tags to a plain text file Besides the gcc that came with the linux I'm using, I've got borland c++ and symantec c++ for windows.
I got them back when I was taking some classes in C programming.

There is a command line in the shell script similar to this for each source file during the compiling stage-

g++ -g -O2 -Wall -MT obj_files/AP_commons.o -MD -MP -MF
"./obj_files/AP_commons.Tpo" -c -o obj_files/AP_commons.o
AP_commons.cpp

Each of those compile commands gets the following error message, and then doesn't produce any output file-

g++: cannot specify -o with -c or -S and multiple compilations

When the link command is run later, there's nothing to link.