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用g ++动态共享库编译(Dynamic Shared Library compilation with g++)

 我正在尝试使用g ++编译以下简单的DL库示例代码，该程序来自Program-Library-HOWTO 。 这只是一个例子，所以我可以学习如何使用和编写共享库。 我正在开发的库的真实代码将用C ++编写。 
 

#include <stdlib.h>
#include <stdio.h>
#include <dlfcn.h>

int main(int argc, char **argv) {
    void *handle;
    double (*cosine)(double);
    char *error;

    handle = dlopen ("/lib/libm.so.6", RTLD_LAZY);
    if (!handle) {
        fputs (dlerror(), stderr);
        exit(1);
    }

    cosine = dlsym(handle, "cos");
    if ((error = dlerror()) != NULL)  {
        fputs(error, stderr);
        exit(1);
    }

    printf ("%f\n", (*cosine)(2.0));
    dlclose(handle);
}

 

 如果我用gcc编译程序，它可以正常工作。 
 

gcc -o foo foo.c -ldl

 

 当我将文件名和编译器更改为以下内容时 
 

g++ -o foo foo.cpp -ldl

 

 我收到以下错误： 
 

 
 
 foo.cpp：16：错误：从'void *'无效转换为'double（*）（double）' 
 

 

 我明白（我想我理解，纠正我，如果这是错误的），我不能从C ++中的void指针隐式转换，但C让我，这就是为什么上面的代码将使用gcc编译但不使用克++。 所以我通过将上面的第16行改为： 
 

cosine = (double *)dlsym(handle, "cos");

 

 有了这个，我得到以下错误： 
 

 
 
 foo.cpp：16：错误：无法在赋值中将'double *'转换为'double（*）（double）' 
 

 

 这些问题可能与我自己对适当的C ++编码标准的一般无知比其他任何事情有关。 任何人都可以点我一个关于开发使用C ++示例代码的Linux动态库的好教程吗？ 

I'm trying to compile the following simple DL library example code from Program-Library-HOWTO with g++. This is just an example so I can learn how to use and write shared libraries. The real code for the library I'm developing will be written in C++.
 

#include <stdlib.h>
#include <stdio.h>
#include <dlfcn.h>

int main(int argc, char **argv) {
    void *handle;
    double (*cosine)(double);
    char *error;

    handle = dlopen ("/lib/libm.so.6", RTLD_LAZY);
    if (!handle) {
        fputs (dlerror(), stderr);
        exit(1);
    }

    cosine = dlsym(handle, "cos");
    if ((error = dlerror()) != NULL)  {
        fputs(error, stderr);
        exit(1);
    }

    printf ("%f\n", (*cosine)(2.0));
    dlclose(handle);
}

 

If I compile the program with gcc it works fine.
 

gcc -o foo foo.c -ldl

 

When I change the filename and compiler to the following
 

g++ -o foo foo.cpp -ldl

 

I get the following error:
 

 
 
foo.cpp:16: error: invalid conversion from 'void*' to 'double (*)(double)'
 

 

I understand (I think I understand, correct me if this is wrong) that I can't do an implicit cast from a void pointer in C++, but C lets me, and this is why the above code will compile using gcc but not using g++. So I tried an explicit cast by changing line 16 above to:
 

cosine = (double *)dlsym(handle, "cos");

 

With this in place, I get the following error:
 

 
 
foo.cpp:16: error: cannot convert 'double*' to 'double (*)(double)' in assignment
 

 

These problems probably have more to do with my own general ignorance of proper C++ coding standards than anything else. Can anyone point me to a good tutorial on developing dynamic libraries for Linux that uses C++ example code?

原文：https://stackoverflow.com/questions/483797
更新时间：2023-04-23 19:04

最满意答案

 我通过实现新的UINavigationControllerDelegate方法animationControllerForOperation解决了这个问题。 
 

 例如： 
 

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController     *)navigationController
                              animationControllerForOperation:(UINavigationControllerOperation)operation
                                           fromViewController:(UIViewController *)fromVC
                                             toViewController:(UIViewController *)toVC
{

PushTransition* transition = [PushTransition new];
[transition setNavigationControllerOperation: operation];

return transition;
}

 

 PushTransition是一个实现UIViewControllerAnimatedTransitioning协议的类，以及该协议中的两个方法transitionDuration和animateTransition。 此外，我添加了一个属性来传递操作（告诉我它是否是推送或弹出过渡）。 
 

 只需将动画代码移动到animateTransition中，如下所示： 
 

// the containerView is the superview during the animation process.
UIView *container = transitionContext.containerView;

UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

UIView *fromView = fromVC.view;
UIView *toView = toVC.view;
CGFloat containerWidth = container.frame.size.width;

// Set the needed frames to animate.

CGRect toInitialFrame = [container frame];
CGRect fromDestinationFrame = fromView.frame;

if ([self navigationControllerOperation] == UINavigationControllerOperationPush)
{
    toInitialFrame.origin.x = containerWidth;
    toView.frame = toInitialFrame;
    fromDestinationFrame.origin.x = -containerWidth;
}
else if ([self navigationControllerOperation] == UINavigationControllerOperationPop)
{
    toInitialFrame.origin.x = -containerWidth;
    toView.frame = toInitialFrame;
    fromDestinationFrame.origin.x = containerWidth;
}

// Create a screenshot of the toView.
UIView *move = [toView snapshotViewAfterScreenUpdates:YES];
move.frame = toView.frame;
[container addSubview:move];

[UIView animateWithDuration:TRANSITION_DURATION delay:0
     usingSpringWithDamping:1000 initialSpringVelocity:1
                    options:0 animations:^{
                        move.frame = container.frame;
                        fromView.frame = fromDestinationFrame;
                    }
                 completion:^(BOOL finished) {
                     if (![[container subviews] containsObject:toView])
                     {
                         [container addSubview:toView];
                     }

                     toView.frame = container.frame;
                     [fromView removeFromSuperview];
                     [move removeFromSuperview];
                     [transitionContext completeTransition: YES];
                 }];

 

 描述它，你可以完成。 另外，你可以制作任何你喜欢的推动或流行动画。 

I solved the problem by implementing the new UINavigationControllerDelegate Method animationControllerForOperation.
 

For example:
 

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController     *)navigationController
                              animationControllerForOperation:(UINavigationControllerOperation)operation
                                           fromViewController:(UIViewController *)fromVC
                                             toViewController:(UIViewController *)toVC
{

PushTransition* transition = [PushTransition new];
[transition setNavigationControllerOperation: operation];

return transition;
}

 

PushTransition is a class that implements the UIViewControllerAnimatedTransitioning protocol and the two methods transitionDuration and animateTransition from that protocol. Additionally, i have added a property to pass the operation (tells me if it is a push or pop transition).
 

Just put the animation code for moving the views into the animateTransition as follows:
 

// the containerView is the superview during the animation process.
UIView *container = transitionContext.containerView;

UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

UIView *fromView = fromVC.view;
UIView *toView = toVC.view;
CGFloat containerWidth = container.frame.size.width;

// Set the needed frames to animate.

CGRect toInitialFrame = [container frame];
CGRect fromDestinationFrame = fromView.frame;

if ([self navigationControllerOperation] == UINavigationControllerOperationPush)
{
    toInitialFrame.origin.x = containerWidth;
    toView.frame = toInitialFrame;
    fromDestinationFrame.origin.x = -containerWidth;
}
else if ([self navigationControllerOperation] == UINavigationControllerOperationPop)
{
    toInitialFrame.origin.x = -containerWidth;
    toView.frame = toInitialFrame;
    fromDestinationFrame.origin.x = containerWidth;
}

// Create a screenshot of the toView.
UIView *move = [toView snapshotViewAfterScreenUpdates:YES];
move.frame = toView.frame;
[container addSubview:move];

[UIView animateWithDuration:TRANSITION_DURATION delay:0
     usingSpringWithDamping:1000 initialSpringVelocity:1
                    options:0 animations:^{
                        move.frame = container.frame;
                        fromView.frame = fromDestinationFrame;
                    }
                 completion:^(BOOL finished) {
                     if (![[container subviews] containsObject:toView])
                     {
                         [container addSubview:toView];
                     }

                     toView.frame = container.frame;
                     [fromView removeFromSuperview];
                     [move removeFromSuperview];
                     [transitionContext completeTransition: YES];
                 }];

 

described it and you can you are done. Additionally you can make any push or pop animation you like.

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