Is a C++ program really slower than a similar C program?

Question

Assume that i have written a program in C++ without using RTTI and run-time polymorphism (no virtual function, no virtual inheritance) and classes don't have private/protected members, also the C++ specific header files are not used (i.e. C header files are used: cstring, cstdio, ... instead of string, iostream, ...).

Then i want to write a similar program in C which the first argument type of the functions are corresponded to the related struct.

For example:

//C++ code

struct Custom
{
    int a;
    Custom() { }
    void change() { }
    ~Custom() { }
};

int main()
{
    Custom m; //init m
    m.change();
    //destroy m
}

/*C code*/

struct Custom
{
    int a;
};
void custom_init(Custom* like_this) { }
void custom_change(Custom* like_this) { }
void custom_destroy(Custom* like_this) { }

int main()
{
    Custom m;
    custom_init(&m);
    custom_change(&m);
    custom_destroy(&m);
}

Is the C++ program slower than the similar C program (Generally)? if yes, why C programs are faster then? I know, C++ uses the RAII design pattern for memory management, is it the reason for the slow?

I heard that some people said the C programs is faster... why?

Edit: Why this question is closed? i wanted to know if c++ does something additionally which we don't need, and how it affects the performance (makes it slower? faster? or nothing?).

Answer 1

This depends on the compiler used. For example, if you compile a C program with a C++ compiler it runs the same.

Answer 2

No, it's almost certainly false. RAII by itself will not make the program slower. Both C and C++ compilers would probably generate almost identical code for these examples.

Answer 3

You'll never know until you try. If the C++ uses anything that C does not (such as constructors, destructors and even non-virtual methods), it may be slower.

But the difference will probably be so small as to be unnoticeable.

Early implementations of C++ may have been slower than C but that's the nature of any software. It improves with time.

Measure, don't guess! Profile your specific code to see which is faster. But even if C code is faster, the price of losing all that extra functionality may be too much. Execution speed is only one speed, and rarely the important one. My opinion of which speed is the most important is development speed.

Answer 4

C++ doesn't use RAII. You CAN use RAII in your c++ program.
As long as you are doing exactly the same thing in C++ and in C, both program should be exactly as fast.
Writing fast programs in C or C++ is not a matter of programming language but of what kind of feature you use.