检测并在Objective-C运行使用可选的外部C库 [英] Detect and use optional external C library at runtime in Objective-C
问题描述
我建立一个SDK的iPhone开发者可以在其项目。这是作为一个编制了。一个无源$ C $ C。让我们把我的SDKAAA。
I am building an SDK that iPhone developers can include in their projects. It is delivered as a compiled ".a", without source code. Let's call my SDK "AAA".
在他的项目的客户（我们称之为BBB），除了使用AAA，也可以使用所谓的CCC第三方库 - 其中还附带pre-编译闭源。我不卖CCC，这是一个不同的公司。
The customer in his project (let's call it "BBB"), in addition to use AAA, may also use a 3rd party library called "CCC" - which also comes pre-compiled, closed-source. I do not sell CCC, it's a different company.
我的SDK，AAA，可以选择使用CCC来改进产品，使用这些第三方功能。例如，假设CCC是一个安全的SDK来加密的东西。 AAA不需要CCC，但会更安全，如果客户选择包括CCC在他们的项目以及
My SDK, AAA, can optionally use CCC to improve the product, using those 3rd party features. For example, let's say CCC is a security SDK to encrypt something. AAA does not require CCC, but will be more secured if the customer chooses to include CCC in their project as well.
现在这里是一个额外的棘手的部分 - CCC库，是纯C code，国产C结构和C函数 - 没有面向对象吧
Now here is an extra tricky part - the CCC library, is pure C code, made of C Structs and C functions - nothing object-oriented about it.
的问题是：
- 如何编译我AAA SDK使用从CCC功能/结构，而不包括在我的项目CCC（而不是法律允许，不想要跟上的最新版本更新）。
- 我如何可以检测如果客户在其项目有CCC，仅可用？ 来使用这些额外的功能
- How can I compile my AAA SDK to use functions/structs from CCC, without including CCC in my project (not legally allowed to, and don't want to keep up to date with version updates).
- How can I detect if the customer has CCC in his project, to use those extra features only if available?
推荐答案
使用 对dlsym 度日函数名的C函数指针。如果能找到他们，他们在那里。否则，他们不是。只需使用 RTLD_DEFAULT 作为第一个参数。
Use dlsym to get the C function pointers by function name. If it can find them, they're there. Otherwise they're not. Just use RTLD_DEFAULT as the first parameter.
编辑：抛下周围的是iOS示例，请参阅迈克灰的<一个href=\"https://www.mikeash.com/pyblog/friday-qa-2012-05-18-a-tour-of-plweakcompatibility-part-i.html\">write达PLWeakCompatibility ，特别是在下降到'一节中。你会看到他检查 objc_loadWeakRetained （运行时调用相关的弱引用）是present。在5+这是和他的版本直接调用真正之一。在4也不是那么他的版本做别的东西来代替。
having cast around for an iOS example, see Mike Ash's write up of PLWeakCompatibility, particularly the section on 'Falling Through'. You'll see he checks whether objc_loadWeakRetained (a runtime call related to weak references) is present. Under 5+ it is and his version calls the real one directly. Under 4 it isn't so his version does something else instead.
EDIT2：样品code：
sample code:
示例1：
#import <Foundation/Foundation.h>
#include <dlfcn.h>
int main(int argc, char *argv[])
{
@autoreleasepool
{
NSLog(@"%p", dlsym(RTLD_DEFAULT, "someFunc"));
}
}
输出为0x0 。示例2：
#import <Foundation/Foundation.h>
#include <dlfcn.h>
void someFunc()
{
}
int main(int argc, char *argv[])
{
@autoreleasepool
{
NSLog(@"%p", dlsym(RTLD_DEFAULT, "someFunc"));
}
}
输出比为0x0以外的地址。
Outputs an address other than 0x0.
示例3：
#import <Foundation/Foundation.h>
#include <dlfcn.h>
void someFunc()
{
NSLog(@"Hi!");
}
int main(int argc, char *argv[])
{
@autoreleasepool
{
void (* func)();
func = dlsym(RTLD_DEFAULT, "someFunc");
func();
}
}
输出你好！。
结构体没有presence在某或其他地方在运行时，他们只是在如何格式化数据的指令编译器。所以你需要包括任何实际的结构或它们在你的code兼容的重述。
Structs have no presence in a .a or elsewhere at runtime, they're just instructions to the compiler on how to format data. So you'll need to include either the actual structs or a compatible restatement of them in your code.
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