C vs C++: the main differences, from an object-oriented point of view
C is a procedural language: programs are functions operating on data structures. C++ began as "C with classes" and keeps almost all of C, adding the tools of object-oriented and generic programming. The differences matter in interviews and when reading older code that mixes the two.
At a glance
| Feature | C | C++ |
|---|---|---|
| Paradigm | Procedural | Multi-paradigm: procedural, object-oriented, generic, functional elements |
| Classes, access control | No (struct holds data only) | class/struct with member functions, public/private/protected |
| Inheritance, virtual functions | No | Yes, including multiple inheritance |
| Function overloading | No | Yes |
| Generic code | Macros, void* | Templates |
| Memory management | malloc/free | new/delete, constructors/destructors, smart pointers |
| Error handling | Return codes, errno | Exceptions (plus return codes) |
| References | Pointers only | Pointers and references |
| Namespaces | No | Yes |
| Standard library | C standard library | C library plus containers, algorithms, strings, streams… |
The same idea in both
/* C: data and functions are separate */
typedef struct { double balance; } Account;
void deposit(Account *a, double amount) { if (amount > 0) a->balance += amount; }// C++: the class bundles data and behaviour and hides the state
class Account {
public:
explicit Account(double opening) : balance_(opening) {}
void deposit(double amount) { if (amount > 0) balance_ += amount; }
double balance() const { return balance_; }
private:
double balance_;
};In the C version any code can write a->balance = -1; in C++ the compiler forbids access to balance_ outside the class. That is encapsulation, the first of the OOP principles explained in OOP concepts with examples.
RAII: the most important C++ idea C lacks
In C++, an object's destructor runs automatically when it goes out of scope. Wrapping a resource in an object (a file, a lock, memory) ties its release to scope: "resource acquisition is initialisation". std::unique_ptr, std::vector and std::lock_guard all work this way, which removes most manual free calls and leaks. C# achieves a similar effect with using and IDisposable, while memory itself is handled by the garbage collector.
Compatibility
Most C code compiles as C++, but not all: C++ is stricter about conversions (for example from void*), reserves more keywords (class, new), and the two standards have diverged on some features since C99. Mixed projects declare C functions with extern "C" so the C++ compiler does not mangle their names.
And C#?
C# borrows its syntax from the C family but runs on a managed runtime: garbage collection, no manual memory management in normal code, single class inheritance with interfaces, generics checked at run time, and a large framework library. See Java vs .NET for how it compares with its closest rival.
References
- Microsoft Learn: C++ language reference, C language reference, Object lifetime and resource management (RAII)
- ISO C++: C++ FAQ