关于可可C风格功能的一些愚蠢的问题

Question

In spite of I'm developing for years in Cocoa, I never have to develop a kind of C-style library for working on non-objects vars.

What I call "C-style functions" is, for example:

float myCStyleFunction(float var1, float var2);

Knowing Objective-C is a descendant of C, I was trying to make a real C function. But some simple things are not permitted by the compilator.

First the pass-by-reference :

void makeSomethingWithImages(CGImageRef & im1, CGImageRef & im1);

This do not work. Compilator says Parameter name omitted . Is there a way to pass-by-reference my CGImages?

Secondly, defaults parameters :

void makeSomethingWithImages(CGImageRef im1, CGImageRef im1, float tolerance) { ... }

void makeSomethingWithImages(CGImageRef im1, CGImageRef im1) {
    makeSomethingWithImages(im1, im2, 0);
}

Error : Conflicting types for 'makeSomethingWithImages'

Is there a way to have some defaults parameters?

And the subsidiary question : if Obj-C is a C descendant, why these examples do not work?

Answer 1

通过引用传递的是C ++而不是c，因此默认参数和函数重载也是如此，尽管clang为函数重载向c添加了扩展名，但是有附加的语法。

Answer 2

Pass by reference shall be using the- * notation( pointer to the Address ), & is a " Value at Address ", CGImageRef is defined as CGImage *CGImageRef; in CGImage.h class so the compiler Err..

Answer 3

No, you can't use by-reference passing mechanism, nor default value for arguments in C. If Obj-C is a descendant of C, this means that legal C code is accepted by Obj-C compilation, not the converse.

But you've made a mistake, by-reference and default values are not available in Objective-C. Both of these constructions are C++ ones, not C ones. There exists a mix of Objective-C and C++, it is called Objective-C++.

Both C++ and Objective-C are descendant of C, so the mix.