通过在Android中C $ C $Ç执行命令 [英] Execute commands via C code in Android

问题描述

我要执行的命令，截图亚行的shell /系统/斌/撷取画面-p /sdcard/img.png进入C.我在寻找相同和我另一个命令一个解决方案，我修改了命令

  EXECL（/系统/斌/撷取画面，-p，存储/ sdcard0 / screenShot.png（字符*）NULL）;
 

但是当我运行上述命令我的应用程序和呼叫的方法，应用程序得到崩溃。

我应该如何修改 /系统/斌/撷取画面-p /sdcard/img.png 命令，从C code运行。

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汤姆回答后更新

应用是越来越再次关闭，这里是日志

  11月6日至21日：52：01.488：我/的WindowState（279）：WIN死亡：窗口{40fed2c0 U0 com.mytest.ndktestapplication / com.mytest.ndktestapplication.MainActivity}
11月6日至21日：52：01.498：I / ActivityManager（279）：进程com.mytest.ndktestapplication（PID 7745）已经死亡。
11月6日至21日：52：01.498：W / ActivityManager（279）：强制删除ActivityRecord {40ea9ab8 U0 com.mytest.ndktestapplication / .MainActivity}：应用程序死了，没有保存的状态
 

解决方案

这是EXEC的预期效果（）系列的功能。

他们所做的就是替换当前程序的指定的一个。所以，再见应用程序。

要避免这种情况，你首先需要调用fork（），然后调用exec（）只在孩子，像这样：

 如果（！叉（））{
    // fork（）的返回零，所以我们是在孩子
    EXECL ...
}
 

您可能还调用exec函数之前做一些清理工作。

注意但是，你将无法从大多数设备的应用程序采取截图，随着应用程序code缺乏这样做的权限的用户ID下运行。但是我依稀记得，有一些的地方运设备没有此功能的权限检查狭窄的时期，所以它可能在这些工作。

I want to execute the screenshot command "adb shell /system/bin/screencap -p /sdcard/img.png" into C. I was searching for the same and I got a solution for another command and I modified the command as

execl("/system/bin/screencap", "-p", "storage/sdcard0/screenShot.png", (char *)NULL);

but when I run my application and call method of above command, application gets crash.

How should I modify the "/system/bin/screencap -p /sdcard/img.png" command to run from C code.

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Update after tom answer

Application is getting closed again and here is log

06-21 11:52:01.488: I/WindowState(279): WIN DEATH: Window{40fed2c0 u0 com.mytest.ndktestapplication/com.mytest.ndktestapplication.MainActivity}
06-21 11:52:01.498: I/ActivityManager(279): Process com.mytest.ndktestapplication (pid 7745) has died.
06-21 11:52:01.498: W/ActivityManager(279): Force removing ActivityRecord{40ea9ab8 u0 com.mytest.ndktestapplication/.MainActivity}: app died, no saved state

解决方案

This is the expected result of exec() family functions.

What they do is replace the current program with the specified one. So bye-bye app.

To avoid that you would first need to call fork(), and then call exec() only in the child, something like this:

if (!fork()) {
    // fork() returned zero, so we are in the child
    execl...
}

You might also have to do some cleanup before calling the exec function.

Note however that you will not be able to take a screenshot from an app on most devices, as application code runs under a user id which lacks the permission to do so. But I seem to recall that there was a narrow period where some devices shipped without permission checks on this functionality, so it might work on those.

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