The Big Programming Thread - Page 38

Thread Rules
1. This is not a "do my homework for me" thread. If you have specific questions, ask, but don't post an assignment or homework problem and expect an exact solution.
2. No recruiting for your cockamamie projects (you won't replace facebook with 3 dudes you found on the internet and $20)
3. If you can't articulate why a language is bad, don't start slinging shit about it. Just remember that nothing is worse than making CSS IE6 compatible.
4. Use [code] tags to format code blocks.

jaydubz

21 Posts

February 16 2011 17:42 GMT

#741

The problem is definitely making sense. I'm going to try to make some tweaks later tonight and see if I can get it to compile. Thanks for the help and suggestions so far!

Pigsquirrel

United States615 Posts

February 17 2011 16:21 GMT

#742

I have a C++ question. How would I go about doing something like this:


#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;

int main () {
  string fileName = "example.txt"
  ofstream myfile;
  myfile.open (fileName);
  myfile << "Writing this to a file.\n";
  myfile.close();
  return 0;
}

It appears the string is the wrong variable type. What type should I use and is it possible anyway?

EDIT Google Came Through:



#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;

int main () {
    string l="example.txt";
    const char *p;
    p=l.c_str();
    ofstream myfile;
    myfile.open (p);
    myfile << "Writing this to a file.\n";
    myfile.close();
    return 0;
}

fabiano

Brazil4644 Posts

February 17 2011 16:34 GMT

#743

If you read the documentation for ofstream::open you will find that the parameter must be a char*, however you are passing a object string.

To make it work, use filename.c_str(), since it returns a char* from your object string.

Frigo

Hungary1023 Posts

February 17 2011 16:34 GMT

#744

fileName.c_str() instead of fileName, this is a small design error of C++

tofucake

Hyrule19193 Posts

February 17 2011 16:41 GMT

#745

It's not a design error.

Also, you need a semicolon.

EscPlan9

United States2777 Posts

February 18 2011 00:51 GMT

#746

On February 18 2011 01:41 tofucake wrote:
It's not a design error.

It's just a pain in the ass and you'll run into the problem a lot. Thank god for the c_str() function! I started off programming in Java, so the whole C-style strings vs Strings thing still is weird to me.

I'm about to begin my first co-op (basically paid internship). I'm seeking one within software development or system administration (my two concentrations within IT). I have a moderate amount of experience with both Java and C++ (just started learning C++ this quarter but it has been easy to pickup), and very minimal with SQL (mySql only), CSS, and HTML. For those who have done internships, could you go into some detail with some of the work you ended up doing? I'm curious the types of things I should be practicing more on before I'm out programming for a company.

heishe

Germany2284 Posts

February 18 2011 01:17 GMT

#747

On February 18 2011 01:21 Pigsquirrel wrote:
I have a C++ question. How would I go about doing something like this:


#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;

int main () {
  string fileName = "example.txt"
  ofstream myfile;
  myfile.open (fileName);
  myfile << "Writing this to a file.\n";
  myfile.close();
  return 0;
}

It appears the string is the wrong variable type. What type should I use and is it possible anyway?

EDIT Google Came Through:



#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;

int main () {
    string l="example.txt";
    const char *p;
    p=l.c_str();
    ofstream myfile;
    myfile.open (p);
    myfile << "Writing this to a file.\n";
    myfile.close();
    return 0;
}

Why do you use <iostream> <fstream> and then <string.h> instead of <string> ?

EscPlan9

United States2777 Posts

February 19 2011 06:24 GMT

#748

I notice a lot of job descriptions ask for a broad range of skills. I'm only good with Java and C++ and know the basics of MySQL, CSS, and HTML. Any suggestions for languages I should learn next? I'm a quick learner especially now that I have a decent "programming mindset" for these things.

IKenshinI

United States132 Posts

February 19 2011 06:39 GMT

#749

On February 19 2011 15:24 EscPlan9 wrote:
I notice a lot of job descriptions ask for a broad range of skills. I'm only good with Java and C++ and know the basics of MySQL, CSS, and HTML. Any suggestions for languages I should learn next? I'm a quick learner especially now that I have a decent "programming mindset" for these things.

Learn C

EscPlan9

United States2777 Posts

February 19 2011 06:45 GMT

#750

I was thinking about C# as one of the next ones I pick up. I read it's sort of like a mix between Java and C++, so should be quick to pickup. Is there a reason I would want to learn C? Does it do something better? It was my understanding that pretty much no company uses C. Rather they want people who know C# and C++ (along with other languages).

Cloud

Sexico5880 Posts

February 19 2011 06:45 GMT

#751

Maybe you want to shift your learning toward a different direction? Try learning Unix, always a good thing to have in your resume:
http://www.catb.org/~esr/faqs/loginataka.html

I think Oracle is a bigger standard than MySQL:
http://philip.greenspun.com/sql/

I can quote Peter Norvig on "teaching yourself programming in 10 years"

Learn at least a half dozen programming languages. Include one language that supports class abstractions (like Java or C++), one that supports functional abstraction (like Lisp or ML), one that supports syntactic abstraction (like Lisp), one that supports declarative specifications (like Prolog or C++ templates), one that supports coroutines (like Icon or Scheme), and one that supports parallelism (like Sisal).

Or an interesting blog post by a rather unknown person http://axisofeval.blogspot.com/2011/01/curing-pl-anxiety.html

And as ESR says, you're only good when you're recognized as good by other good programmers, and the best way to do that is to work on open source projects. Also possibly the very best thing to have in your resume (awesome if your interviewers can google you!)
http://freshmeat.net/

destian

141 Posts

February 19 2011 06:46 GMT

#752

I have a question for anyone who's programming in the MVVM pattern. I'm working on a project that is showing ~30 text fields on a view. I can't help but think there has to be a better way than data binding 30+ properties. This seems wasteful. Any ideas?

Cloud

Sexico5880 Posts

February 19 2011 06:48 GMT

#753

On February 19 2011 15:45 EscPlan9 wrote:
I was thinking about C# as one of the next ones I pick up. I read it's sort of like a mix between Java and C++, so should be quick to pickup. Is there a reason I would want to learn C? Does it do something better? It was my understanding that pretty much no company uses C. Rather they want people who know C# and C++ (along with other languages).

There is one reason to learn C, and it's more than enough: Unix. Now C is not Unix so you actually have to learn Unix and not only C.

destian

141 Posts

February 19 2011 06:49 GMT

#754

If you have good experience with those two languages, it really is trivial to learn similar OOP languages. I'd suggest becoming more fluent in SQL. If you're leaning towards a company IT job, learning pivots in SQL will be invaluable.

haduken

Australia8267 Posts

February 19 2011 12:27 GMT

#755

On February 19 2011 15:46 destian wrote:
I have a question for anyone who's programming in the MVVM pattern. I'm working on a project that is showing ~30 text fields on a view. I can't help but think there has to be a better way than data binding 30+ properties. This seems wasteful. Any ideas?

30 text fields? Why not just show a grid?

haduken

Australia8267 Posts

February 19 2011 12:28 GMT

#756

Does anyone here use DevExpress winform? Why the hell does it crashes VS designer all the time...

KaiserJohan

Sweden1808 Posts

February 19 2011 17:49 GMT

#757

Just curious, what is there to learn in C when you know a moderate amount of C++?

I can understand there might be different design issues, for example using structs instead of classes. But anything else? Learning unix libraries? :S

Also--- would it be wise to use the string class in c++, and then to go through the string use a string iterator? Instead of the traditional way with C strings, I'm wondering which one is the standard in industry: C++ strings or C strings, for C++ programming.
For example I can guess c++ string operations will be slower than on C-type strings, but it risk give you buffer overflows or alike.

heishe

Germany2284 Posts

February 19 2011 18:01 GMT

#758

When you learn C (as someone who already knows C++), you don't actually learn a new language, you learn how to use a new programming paradigm (strictly structured instead of object oriented programming).

C as a language is syntactically identical to C++. C's grammar (the grammar of its formal language) and it's standard library of course have a lot of stuff missing that C++ has (classes etc., all of the stuff that comes with the STL, also C has no bool

), but other than that they're completely similar.

On February 20 2011 02:49 KaiserJohan wrote:

For example I can guess c++ string operations will be slower than on C-type strings, but it risk give you buffer overflows or alike.

The c++ string class can be accessed like a c-type string without any performance disadvantages:


#include <string>
#include <iostream>

void foo()
{

   std::string my_string = "abcd"; //my_string("abcd") works too.
   
   std::cout<<my_string[2]<<std::endl; //prints "c" followed by a new line
}

There should be no performance disadvantages using the [] operator as opposed to using iterators.

I'm not entirely sure, since I don't know the implementation of std::string, but the [] operator probably even is faster than iterating through the single chars manually.

Why do I think so? Well, internally std::string probably just manages a standard c-type array, which would make it's [] operator implementation as simple as this:


char operator[] (int i)
{
    return m_ctype_char_array[i];
}

If you'd use iterators, you'd have to iterate through every char manually, which of course would be much much slower.

Note that your program will cause undefined behaviour if you try to access something outside the strings range, too, since std::string provides no protection from reading out of range stuff manually. When you iterate through the string using std::string::iterator or const_iterator manually, you can also acces stuff that is out of range by iterating "too far". Nothing saves you from that, as far as I'm aware.

As for your question:

On February 20 2011 02:49 KaiserJohan wrote:
Also--- would it be wise to use the string class in c++, and then to go through the string use a string iterator? Instead of the traditional way with C strings, I'm wondering which one is the standard in industry: C++ strings or C strings, for C++ programming.

In your usual application, of course using std::string is standard. It's just much more comfortable to use and provides a lot of functionality that an ordinary c-type char array doesn't have ( string a += "attachment"; for example )

But if you develop something in C++ where performance is really important (especially if you're trying to keep memory usage down) or where you don't need the extra std::string functionality, you might want to consider using standard c-type strings.

For example, if you just need the location of a file in a given method, you should consider using


void foo(const char *filename)
{
   std::ofstream off(filename);
   //do something with the file
   o.close();
}

instead of using


void foo(std::string filename)
{
    std::ofstream off(filename.c_str());
    //do something with the file
    o.close();
}

since std::string carries a very small (bet still existing) overhead compared to c-style strings in terms of memory usage.

filename.c_str() shouldn't be slower than directly handing over a const char *filename, since filename.c_str() should be inlined by your compiler, however, copying a string "into the method" when calling it might actually be slower than copying the pointer to a c-type char array, however I'm not sure about that.

KaiserJohan

Sweden1808 Posts

February 20 2011 12:29 GMT

#759

I see, thanks for the clarification!

EscPlan9

United States2777 Posts

February 21 2011 07:04 GMT

#760

I struggle a lot with fully grasping double linked lists using nodes in C++. I end up trying to draw everything out, a lot of scribbles, taking dozens of minutes designing out how I should be implementing it, and then still struggling when my design doesn't pan out. Any advice for how to get a better grasp on using double linked lists?

I'll be seeing my professor again tomorrow to help me better understand this. Just curious what any of you would recommend for getting better at it.

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