Vectors work when they want to.

Makes 0% sense.

I understood and still understand how to make vectors, but now it doesn't work, what the hell?

push_back is acting like a dick, it gives me an error when I try to call it, even though it's been called like this before, pfft.. It's weird.

Code:

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#include <string>
#include <vector>

std::vector<int> vec;

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Yes we know this works, and push_back works.

Code:

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vec.push_back(12);

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But this doesn't work, and I even used vectors before, and even used this, now it doesn't work. Lol C++ is REEEEAALLY GREAT

Post the errors you're getting and tell us how it's "not working".

std::vector<int> vec();

Very rarely does a language "act like a d***"

Code:

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1>(6) : error C2143: syntax error : missing ';' before '.'
1>(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>(6) : error C2371: 'test' : redefinition; different basic types
1>        (4) : see declaration of 'test'

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The code that's failing to compile would help, too.

Quote:

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Originally Posted by medievalelks

The code that's failing to compile would help, too.

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It was in the OP..

Fine..

Code:

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#include <string>
#include <vector>

std:: vector<int> vec;

vec.push_back(12);

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The compiler is complaining about something named "test". I don't see that in the code.

Quote:

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Originally Posted by medievalelks

The compiler is complaining about something named "test". I don't see that in the code.

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That's because I'm changing code around. :P Basically, it's the same thing every time, regardless of what the variable name is.

Wow.. Even copy-pasted code from cppreference.com doesn't even work. wtf?

There is a space between your declarations std:: and the vector object

Quote:

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Originally Posted by swgh

There is a space between your declarations std:: and the vector object

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So? It worked liked that before so it doesn't matter. And others work aswell so meh.

Just a number '12' can be seen as a 'const int' , in which case your specialisation is not correct. Try to define an int equal to 12, and then push back that int. Although I don't suspect this from being the error...

Code:

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std::vector<int> vec();

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this shouldn't make any difference...

Post the complete piece of code you're trying to compile, not just snippets. And if you're copy-pasting code, you have to be careful that you don't get any hidden HTML chars in it.

Quote:

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Originally Posted by MarkZWEERS

Just a number '12' can be seen as a 'const int' , in which case your specialisation is not correct. Try to define an int equal to 12, and then push back that int.

Code:

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std::vector<int> vec();

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this shouldn't make any difference...

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Neither std::vector<int> vec(); nor const work.

Quote:

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Originally Posted by indigo0086

std::vector<int> vec();

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That's a declaration of a function named vec that takes no arguments and returns a std::vector<int>.

Quote:

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Originally Posted by medievalelks

Post the complete piece of code you're trying to compile, not just snippets. And if you're copy-pasting code, you have to be careful that you don't get any hidden HTML chars in it.

---

Code:

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#include <vector>
#include <iostream>
std::vector<int> vec;
vec.push_back(1);

/*
Errors:

1>(4) : error C2143: syntax error : missing ';' before '.'
1>(4) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>(4) : error C2371: 'vec' : redefinition; different basic types
1>        (3) : see declaration of 'vec'

*/

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Ehm.. have you created a function 'int main()' ?

This works fine on VC++

Code:

---

#include <iostream>
#include <vector>

int main()
{
  std:: vector<int> vec;

  vec.push_back(12);
 
  for ( int i = 0; i < vec.size(); i++ )
  {
      std::cout << vec[ i ] << " ";
  }
 
  std::cin.get();
 
  return 0;
}

---

Output is 12 as it should be

Quote:

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Originally Posted by swgh

This works fine on VC++

Code:

---

#include <iostream>
#include <vector>

int main()
{
  std:: vector<int> vec;

  vec.push_back(12);
 
  for ( int i = 0; i < vec.size(); i++ )
  {
      std::cout << vec[ i ] << " ";
  }
 
  std::cin.get();
 
  return 0;
}

---

Output is 12 as it should be

---

Well the int main made it work, but I've had it where it works without the int main, what is wrong with C++???

Proof it works without int main:

http://cboard.cprogramming.com/showthread.php?t=105607

What do you expect your computer to execute when there is no function 'main' ? There is something wrong with your code and your knowledge of C++, not of C++ itself..

Every single C.C++ program needs a main function. It is the starting location and the first function called by the operating system. 99&#37; of the time no C++ program will compile without a main function. The OS needs to know where to start from.

Maybe it's not weither it's in the scope or not, but weither the int main is even called.

Edit: doesn't work tohugh, wtf????

Quote:

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Originally Posted by swgh

Every single C.C++ program needs a main function. It is the starting location and the first function called by the operating system. 99% of the time no C++ program will compile without a main function. The OS needs to know where to start from.

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Even the big programs? Like Firefox?

Why are you trying to create a program without main()? Its bad practice anyway, and all good up to date compilers will forbid it unless you have some special setting or circumstance on when main will not be called

You can also just create shared object libraries (.so , Unix/Linux), or dynamic link libraries (.dll , windowz) , which are loaded in some platform or by another program. But then, that program does have a function main.

No main no brain

Quote:

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Originally Posted by swgh

Why are you trying to create a program without main()? Its bad practice anyway, and all good up to date compilers will forbid it unless you have some special setting or circumstance on when main will not be called

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It's not that, it's just that it seems I get errors when I try to do stuff outside the int main, go check out my other thread about vectors and windows, I have the vector outside the main, and after I fixed it up from the other errors, it worked fine outside the int main, so whats the deal?

It could have been defined in the scope of a free function and compiled with -c - i.e., no main() function needed.

But to the OP, how and when did you expect that code to get executed if it wasn't in main() or any other function?

Quote:

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Originally Posted by medievalelks

It could have been defined in the scope of a free function and compiled with -c - i.e., no main() function needed.

But to the OP, how and when did you expect that code to get executed if it wasn't in main() or any other function?

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Well I know int main is the main ( -_- ) function that executes it all, but I didn't know it is that strict.

The C++ standard has many rules and definitions over main. Main is like the heart of a program. It can ( and somtimes does ) call a single function. But without it, nothing would work. Remember, unless told otherwise by a called function, a program will also terminate via main's return statement.

Quote:

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Originally Posted by swgh

The C++ standard has many rules and definitions over main. Main is like the heart of a program. It can ( and somtimes does ) call a single function. But without it, nothing would work. Remember, unless told otherwise by a called function, a program will also terminate via main's return statement.

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Okay. So why does the main be an int? why not.. char?

Read the FAQ

Basically, in C++ you can't put any code (unless it is a definition or declaration) outside functions. All that the program does happens within one function or another.

So your problem has nothing to do with vector specifically.

Code:

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#include <iostream>
int a = 1; //declare a global variable, OK
a += 1; //nope, can't do this outside functions
std::cout << a << '\n'; //nor this

---

Quote:

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Originally Posted by anon

Basically, in C++ you can't put any code (unless it is a definition or declaration) outside functions. All that the program does happens within one function or another.

So your problem has nothing to do with vector specifically.

Code:

---

#include <iostream>
int a = 1; //declare a global variable, OK
a += 1; //nope, can't do this outside functions
std::cout << a << '\n'; //nor this

---

---

Ah, okay.. Thanks..

>> Proof it works without int main:
>> http://cboard.cprogramming.com/showthread.php?t=105607

It didn't work there either:
http://cboard.cprogramming.com/showthread.php?p=775417

It's not that the compiler doesn't like you, it's just like a big ole calculator. If you push the wrong buttons it gives you the wrong answer. If you write a program that doesn't adhere to the rules of the language then it will not compile. Every program needs an entry point, programs don't just start wherever they feel like it. If you don't have an int main then it just wont run.
You can call your compiler or the C++ language names as much as you like until you're blue in the face, it doesn't care. But if you want to do programming you just have to obey the rules of the language, that's just how it is. You're free to complain and protest loudly about your code not compiling, if you must, but if your goal is to learn to program then it wont help you. What will help is having plenty of reference material handy.

This is a basic question, but why would we want to use vectors when it seems a linked list does the same thing?

Put another way, why use linked lists when vectors do the same thing??

Quote:

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Originally Posted by zodiacWarrior

This is a basic question, but why would we want to use vectors when it seems a linked list does the same thing?

Put another way, why use linked lists when vectors do the same thing??

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No, they are very different things. Here's some homework for you:

1. What does it take to remove an item from the start of a vector, and how long does that take compared to a list when there are 1 million items?
2. I want to lookup the value of item 999999 in the above list or vector. Which one is faster, and why?
3. I have a number of pointers to the items in my list/vector and I want to remove an item. For which one of these will that cause problems?

Quote:

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Originally Posted by zodiacWarrior

This is a basic question, but why would we want to use vectors when it seems a linked list does the same thing?

Put another way, why use linked lists when vectors do the same thing??

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Vectors are random access -- you can do vec[6], and get the seventh element in the vector, in constant time. To get the seventh element of a linked list you have to go through the first six and follow the links. (And as 6 becomes 60, or 600, you can imagine what will happen.)

Inserting into the middle of a linked list is easy. Inserting into the middle of a vector is a pain.

Thanks for the info.

How difficult is it to search in a vector? Say I have a vector x = [ 1, 3, 5, 2, 5, 5] and I want to know in which indices, if any, the number 5 occurs. Would that be difficult?

Quote:

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Originally Posted by zodiacWarrior

Thanks for the info.

How difficult is it to search in a vector? Say I have a vector x = [ 1, 3, 5, 2, 5, 5] and I want to know in which indices, if any, the number 5 occurs. Would that be difficult?

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vectors aren't sorted, so you'd have to loop through the entire vector. That's not "difficult", it just takes a little while.

In this case, a map would be better.
There are lots of different containers that seem to do the same thing, but have different strengths and weaknesses. Your job as a programmer is to use the correct tool for the job.