Objective-C检查是否定义了结构

Question

My iOS application can use an optional external 3rd party library.

I thought of using this answer ( Weak Linking - check if a class exists and use that class ) and detect if the class exists before executing code specific to this library.

However, I found out that this external library is not written as Objective-C classes, but rather as C STRUTS and functions.

Is there a similar technique that would allow me to check if a C Strut or function exists? Or some better alternative to see if this library is present at runtime?

Answer 1

struct s are compile-time artifacts. They tell the compiler how to lay out a region of memory. Once that is done, struct s become unnecessary. Unlike Objective-C classes which have metadata, structs have no runtime presence. That is why it is not possible to detect them at runtime.

You can check if a dynamic library is present by calling dlopen , and passing its path:

void *hdl = dlopen(path_to_dl, RTLD_LAZY | RTLD_LOCAL);
if (hdl == NULL) {
    // The library failed to load
    char *err = dlerror(); // Get the error message
} else {
    dlclose(hdl);
}

If dlopen returns NULL , the library cannot be loaded. You can get additional info by calling dlerror . You need to call dlclose after you are done.

Answer 2

AFAIK a classical C function has to exist. It is statically bound during the linking process and it is not, like Objective-C mehtods, dynamically bound on runtime.

So when the code compiles AND links without errors or warnings, then you should be fine.

The same for structs.