C-like procedures in C++? - c++

Question

Does the C++ correct programming style demand writing all your code with classes or are C-like procedures allowed ? If I were to give some code to someone else, would it be accepted as C++ just because it has std::vector and std::string (instead of char *) inside, or everything has to be a class?
eg:
int number = 204;
std::string result = my_procedure(number);
OR
MyClass machine;
std::string result = machine.get(number);
Are there cases where the programmer, will have to, or is allowed to have C-like procedures in some of his source code ? Did you ever had to do something like that?
In the context of this question where does the margin between C and C++ exist (if any)?
I hope my question is clear and inline with the rules.

Answer 1

It's certainly OK to have free functions in your code -- this is a matter of architecture, not of "++ness". For small programs it doesn't even make sense to go all-in with classes, as OO is really a tool to manage complexity. If the complexity isn't there to begin with, why bother?
Your second question, where is the line drawn, doesn't have a short answer. The obvious one is that the line is drawn in all places where the C standard differs from the one for C++. But if you are looking for a list of high-level language features that C++ has and C does not, here are some of them:
Class types and OO (of course)
The STL
Function/operator overloading
References
Templates
new/delete to manage memory

Answer 2

C++ is a multi-paradigm language, where OO, procedural, generic/generative and - to a lesser (but increasing with C++0x) extent functional - are among the paradigms. You should use whichever is the best fit for the problem: you want the code to be easy to get and keep right, and hard to stuff up.
The utility of classes is in packaging data (state) along with the related functions. If your wordify function doesn't need to retain any state between calls, then there's no need to use a class/object. That said, if you can predict that you will soon want to have state, then it may be useful to start with a class so that the client code doesn't need to change as much.
For example, imagine adding a parameter to the function to specify whether the output should be "first", "second" instead of "one", "two". You want the behaviour to be set once and remembered, but somewhere else in the application some other code may also use the functionality but prefer the other setting. It's a good idea to use an object to hold the state and arrange it so each object's lifetime and accessibility aligns with the code that will use it.
EDIT:
In the context of this question where does the margin between C and C++ exist (if any)?
C++ just gives you a richer set of ways to tackle your programming tasks, each with their necessary pros and cons. There are plenty of times when the best way is still the same way it would have been done in C. It would be perverse for a C++ programmer to choose a worse way simply because it was only possible in C++. Still, such choices exist at myriad levels, so it's common to have say a non-[class-]member function that takes a const std::string& parameter, combining the procedural function call with object-oriented data that's been generated by a template: it all works well together.

Answer 3

C++ allows a variety of programming styles, procedural code being one of them.
Which style to use depends on the problem you are trying to solve. The margin between C and C++ is are you compiling your code with a C++ compiler.
I do at times use procedural functions in my code. Sometimes it best solves the problem.

Answer 4

C++ code can still be valid C++ code even without classes. Classes are more of a feature, and are not required in every piece of code.
C++ is basically C with more features, so there isn't really a "margin" between the two languages.

Answer 5

If you read Stroustrup's Design and Evolution, you'll see that C++ was intended to support multiple programming styles. Use whichever one is most appropriate the problem (not the same as always just usnig the one you know.)
In legacy real world applications, there is often very little distinction. Some C++ code was originally C code nad then recompilied. Slowly it migrates to use C++ features to improve its quality.
In short, Yes, C++ code can be procedural. But you'll find it does differ from C code if you use C++ features where appropriate.
What is good practice needs to consider things like encapsulation, testability, and the comprehensibility of the client API.

Answer 6

#include <sstream>
#include <string>
#include <iostream>
using namespace std;
string wordify(int n)
{
stringstream ss;
ss << n; // put the integer into the stream
return ss.str(); // return the string
}
int main()
{
string s1 = wordify(42);
string s2 = wordify(45678);
string s3 = wordify(-99);
cout << s1 << ' ' << s2 << ' ' << s3 << '\n';
}