use protobuf on iphone app

November 30, 2011

This post is a step by step tutorial showing how to use protobuf in iphone application. It shows how to:

  • Create a reusable static library
  • Create a executable project
  • Mix C++ code with object C code

1. Start terminal, cd to root folder of protobuf and run ./configure here to generate config.h header file and makefile.

2. Start XCode and create a new project. Select iOS – Library – Cocoa Touch Static Library project template.

3. Right click Other Sources and select add Existing Files.

4. Select the src/google directory, and add the directory recursively.

5. In the previous step, we add too much source files than actually needed. The sources files for the protoc compiler and unittest are included too. They’re not needed to run ios application. To filter out unnecessary files, we can refer to the libprotobuf_lite_la_SOURCES and libprotobuf_la_SOURCES variables in src/Makefile, which list source files needed for protobuf library.

6. Now we need to add header file search path. Click Edit Project Settings under Project menu item.

7. Double click Header Search Paths.

8. Add protobuf and protobuf/src directory.

9. Now build the project.

10. In the terminal, run “make install” command to build protoc compiler and install it to default location(/usr/local/bin/protoc).

11. Go to examples directory and run “protoc addressbook.proto –cpp_out=./” to generate and addressbook.pb.h files.

12. Create a Window-Based Application.

13. Add reference to the static library we built. Right click Frameworks and select Add Existing Frameworks.

14. Click Add Other button.

15. Select the libprotobuf_ios.a file and click add button. Also, we need to add protobuf/src and protobuf/examples directory to Header Search Paths for this project.

16. Rename add_personAppDelegate.m to so that it’ll be compiled as object C++.

17. The basic logic of is first create the addressbook.dat file in iphone’s document directory. Then create a new AddressBook instance and add a person to it. Finally serialize the addressbook to the file we created. The full source is :

#import “add_personAppDelegate.h”

#include “addressbook.pb.h”
#include <fstream>

using namespace std;

@implementation add_personAppDelegate

@synthesize window;

#pragma mark –
#pragma mark Application lifecycle

– (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {  

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentDirectory = [paths objectAtIndex:0];
    NSString *filename = [NSString stringWithFormat:@”%@/addressbook.dat”, documentDirectory];   

    ifstream input([filename UTF8String], ios::in | ios::binary);   

    tutorial::AddressBook address_book;  
    int count = address_book.person_size();  
    tutorial::Person *person = address_book.add_person();

    tutorial::Person_PhoneNumber *pn = person->add_phone();


    fstream output([filename UTF8String], ios::out | ios::trunc | ios::binary);

    // Override point for customization after application launch.   

    [self.window makeKeyAndVisible]; 

    return YES;

– (void)applicationWillResignActive:(UIApplication *)application {
     Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
     Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.

– (void)applicationDidEnterBackground:(UIApplication *)application {
     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
     If your application supports background execution, called instead of applicationWillTerminate: when the user quits.

– (void)applicationWillEnterForeground:(UIApplication *)application {
     Called as part of  transition from the background to the inactive state: here you can undo many of the changes made on entering the background.

– (void)applicationDidBecomeActive:(UIApplication *)application {
     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

– (void)applicationWillTerminate:(UIApplication *)application {
     Called when the application is about to terminate.
     See also applicationDidEnterBackground:.

#pragma mark –
#pragma mark Memory management

– (void)applicationDidReceiveMemoryWarning:(UIApplication *)application {
     Free up as much memory as possible by purging cached data objects that can be recreated (or reloaded from disk) later.

– (void)dealloc {
    [window release];
    [super dealloc];


18. After build and run the application in iphone emulator, we get generated addressbook.dat file in /Users/user_name/Library/

Application Support/iPhone Simulator/4.3/Applications/9AF109CF-1B33-49DA-BE73-603CC798408F/Documents/addressbook.dat

port protobuf-lite to wince

November 25, 2011

protobuf is a wonderful project that helps us implement communication protocol. There are a lot of benefits to use it in practical project, including:

  1. It has an efficient binary serialization algorithm
  2. It runs cross platforms
  3. It support mainstream programming languages, c++, python and java. there are also lots of porting out there for other popular languages.
  4. It’s designed to make protocols both backward and forward compatible.
  5. It enables developers to focus on protocol design.

 Currently, there is no official windows CE version for protobuf. It’s not an easy task to port protobuf full version to windows CE. But the lite version, which supports less feature than full version (check the explanation for optimize_for option in this page for what’s the difference), is easier to port. Here is how I port it:

  1. Create a Win32 Smart Device Project library project, name it protobuf-lite-ce
  2. Copy all source files from protobuf-lite project to protobuf-lite-ce project in Solution Explorer
  3. Create a ce_port folder in the project’s directory, and copy the errno.h header file from (Visual_Studio_Root)/VC/include into the folder. This is because Windows CE doesn’t have this file, so we need to provide one. Actually, this errno.h can be a pure empty file.
  4. Add “../src;.;./ce_port” to the project’s Additional Include Directories.
  5. The windef.h header file already defines OPTIONAL macro, it conflicts with Cardinality::OPTIONAL enum. So the fails to compile, to solve this, add following code before enum Cardinality definition to undefine OPTIONAL:

#if defined(OPTIONAL)
#if defined(_MSC_VER)
#pragma message (“Unexpected OPTIONAL macro definition, #undefine OPTIONAL”)
#warning  “Unexpected OPTIONAL macro definition, #undefine OPTIONAL”
namespace {

enum Cardinality {

}  // namespace

Now the protobuf-lite-ce project should compiles fine.
Here is the project file for downloading. Just get everything there and place them in protobuf/vsprojects/ directory.

why can we use printf without including stdio.h

October 31, 2011

I read the c programming language again to mourn Dennis Ritchie who passed away recently.

I noticed below statements in section “4.2 Functions Returning Non-integers”, which explains the question, why can we use printf without including stdio.h.

The function atof must be declared and defined consistently. If atof itself and the call to it in main have inconsistent types in the same source file, the error will be detected by the compiler. But if (as is more likely) atof were compiled separately, the mismatch would not be detected, atof would return a  double that  main would treat as an  int, and meaningless answers would result. 
In the light of what we have said about how declarations must match definitions, this might seem surprising. The reason a mismatch can happen is that if there is no function prototype, a function is implicitly declared by its first appearance in an expression, such as
   sum += atof(line)
If a name that has not been previously declared occurs in an expression and is followed by a left parentheses, it is declared by context to be a function name, the function is assumed to return an  int, and nothing is assumed about its arguments. Furthermore, if a function declaration does not include arguments, as in
   double atof();
that too is taken to mean that nothing is to be assumed about the arguments of atof; all parameter checking is turned off. This special meaning of the empty argument list is intended to permit older C programs to compile with new compilers. But it’s a bad idea to use it with new C programs. If the function takes arguments, declare them; if it takes no arguments, use

So, let’s take a look at the hello world sample below:

1 //#include  <stdio.h>
3 int main(int argc, char *argv[])
4 {
5     printf(“hello world!\n);
6     return 0;
7 }

When the code is compiled, the statement on line 5 implicitly declares the printf function because it’s not declared explicitly. It’s the same as if we declared printf as:
  int printf();
And there is no assumption about its argument, so the code can pass the compile phase.

In link phase, unlike c++, only the function name (function signature doesn’t matter) affects the symbol name. So the printf symbol name can be found from the standard c library which is linked automatically. As a result, the code above can compile and run successfully.

stream audio via udp on android

October 24, 2011

In this post, I tried to play small audio data chunks with AudioTrack to show the feasibility of streaming audio. It’s not straightforward enough. So I updated the sample code to actually transfer audio data with udp.
As the image below shows, the application is not too complicated.

The two buttons will each create a new thread to send and recv audio data respectively. And the sender will read audio data from the file /data/1.wav. Then, it sends the data to udp port 2048 on localhost. The receiver reads on 2048 port and feed data received to AudioTrack object.
Full code is available at:

modify CE code for our platform

August 1, 2011

A majority of windows CE core and drivers code is available to us, they reside in public directory of CE installation folder. Occasionally, we may want to modify that part of code, either to change some system behaviors, or add some log messages for debugging our platform’s code.
It’s strongly recommended not to change the original code in place. Because this part of code is shared by all platforms. All platforms will be affected by the modification. The right way is before making any change, copy the module into our own platform directory, and modify the copy there.
Let’s say we want to modify public/common/oak/bootpart module’s code.
1. We first copy it into platform/platform_name/src/common/bootpart
2. Exclude public/common/oak/bootpart from our build

3. Include  platform/platform_name/src/common/bootpart into our build

4. The last step is to update other modules’ sources file. For any module that depends our modified bootpart module, we should change its sources file so that it can find the new bootpart instead of the original bootpart shipped with CE. For instance, change $(_COMMONOAKROOT)\lib\$(_CPUINDPATH)\bootpart.lib to $(_TARGETPLATROOT)\lib\$(_CPUINDPATH)\bootpart.lib     

addr2line for windows

June 28, 2011

While debugging os or application crash bug on windows ce (the tool winaddr2line isn’t particularly used for windows CE application, it can be used for normal windows application too.) platform, developers may not always have the luxury to debug step by step within a IDE. Most of time, the only information available to us is the output on serial port. (It’s already very fortunate if we can see serial port output every time a crash happens.) What we get is something like:

Exception ‘Data Abort’ (4): Thread-Id=06890fba(pth=88eb8948), Proc-Id=06750f9e(pprc=88eb8828) ‘test.exe’, VM-active=06750f9e(pprc=88eb8828) ‘test.exe’
PC=00011048(test.exe+0x00001048) RA=00011018(fff.exe+0x00001018) SP=0002fb98, BVA=00000000

Unhandled exception c0000005:
Terminating thread 88eb8948

Given the PC register value, we need to figure out on while line in our code did the application crash. winaddr2line makes it an easy task as long as we have the pdb symbol file for the application. It’s a attempt to port addr2line to windows world.
Let’s take the preceding log for example. In order to find out the line number of the code that incurs the crash, we need following information.

  1. In which module did the crash happen
  2. What’s the address can we use to query

For question 1, the module name is already available in the log. In our example, it’s test.exe. For question 2, we can see the PC register’s value is 0x00011048. So, we run “winaddr2line.exe -e test.exe 11048 -a -p -s -f” command, and get this: “0x00011048: foo::crash at test.cpp:8”. Now we open test.cpp and check what’s around line 8, the root cause is very obvious.

 2 class foo
 3 {
 4     public:
 5         void crash()
 6         {
 7             int *a = NULL;
 8             int b = *a;
10 };
12 int main ( int argc, char *argv[] )
13 {
14     foo f;
15     f.crash();
16     return 0;
17 }        

In order for the preceding command to work correctly, we must make sure the test.exe and its symbol file test.pdb is available in current directory of the shell that we run winaddr2line. If it’s not the case, we should pass correct path to test.exe for -e argument and path to directory containing test.pdb for -y argument respectively.

In the example, we use PC register’s value directly to query line number. But it’s not always the case. Consider the crash log below:

Exception ‘Raised Exception’ (-1): Thread-Id=06891422(pth=88eb8948), Proc-Id=0675143e(pprc=88eb8828) ‘test.exe’, VM-active=0675143e(pprc=88eb8828) ‘test.exe’
PC=4006d270(coredll.dll+0x0005d270) RA=80118a60(kernel.dll+0x00007a60) SP=0002fb8c, BVA=00000000

Unhandled exception c0000094:
Terminating thread 88eb8948

The crash occurred in coredll.dll module. We run command “winaddr2line.exe -e coredll.dll 4006d270 -a -p -s -f”, but we can see it fails to find the line number. This is because we can’t use the PC register’s value directly here. The coredll.dll is loaded at 0x40010000 (0x4006d270-0x0005d270), which is different from its preferred ImageBase address (0x10000000, which can be examined with “dumpbin /headers coredll.dll” command). And winaddr2line can only make use of the ImageBase address contained statically in PE header of the binary. So, we must change the address to 0x1005d270 (0x10000000+0x0005d270). By using this address, we can see the crash occured at: d:\dublin2-1\private\winceos\coreos\core\dll\crtsupp.cpp:240

Source code for winaddr2line:


June 1, 2011

One of the most used function on a pc is switching between tasks. We may write some code in vim, switch to firefox to search for the usage of an api. And then switch back to vim continue writing code. Most of time, we do this by using Alt+Tab key combination. But it’s not an efficient way if there are many tasks running. It’s not quick enough to find the target task.

The main drawback with Alt+Tab is it forces us to deal with more problems. For example, we want to switch to firefox task, the essential problem we’re dealing with is finding the task using the clue “FIREFOX”. After we press Alt+Tab, we get a window list in which all tasks are identified by icons. Now, we have to deal with another problem, finding out the icon that represents firefox. That’s to say, our brain has to do a “context switch” from the “word processing” problem to an “image recognition” problem.

It’s not intuitive at all. The idea of QuickSwitch is very similar to Spotlight on mac and FuzzyFinder on vim. We can keep concentrating on the “word processing” problem, no context switch.

QuickSwitch runs as a daemon. By using it, at any time we want to switch ao another task, press Ctrl+Alt+S key combination to bring up the QuickSwith main window, in which all tasks are listed. Then, type any part of the window title of the desired task and press enter to switch to it.

For instance, if we want to switch to firefox task. Type “firefox” in the input box. As we type, the window list is filtered. Those windows don’t contain the word we typed in title are filtered out. When there is only one result left in the list, we can press enter key once to switch to it. If there are more than one one result left, we can continuing typing more characters to filter out more un-desired tasks. Or we can press enter to bring focus to the result list and use up, down keys (or Ctrl+P, Ctrl+N) to select desired task and press enter again to switch to it.

Source code:

extend windows ce platform with oalioctl

April 15, 2011

Though not being a open source platform, windows ce is designed to be flexible so that device venders can extend it easily. oalioctl is a feature that makes it possible to do things in kernel space on behalf of application.

1. Extensibility
The essential feature of oalioctl is it enables us to extend windows ce kernel’s functions, and new functions are directly accessible to application layer developers.
2. Separation
oalioctl is completely separated from kernel source code. From the sense of code organization, it doesn’t differ from a normal device driver. The separation makes it easy to maintain and port oalioctl module.
3. Easy to use

Compared to a normal ce driver, the usage of oalioctl is easier from an application developer’s perspective. In order to make use of a normal driver, application usually follows below sequence:
CreateFile -> DeviceIoControl -> CloseHandle
But the application can simply call KernelIoControl to make use of oalioctl library, which is a far more easy way.

oalioctl is implemented as a standalone dynamic library. And it will be loaded automatically during kernel initialization (relevant code is in LoaderInit() function in X:\WINCE600\PRIVATE\WINCEOS\COREOS\NK\KERNEL\loader.c). So it’s not necessary to register this module in platform.reg as other stream drivers do.
When an application calls KernelIoControl, the call stack goes like this:

IOControl //our own oalioctl.cpp
OEMIOControl  // platform/common/src/common/ioctl/ioctl.c
IOControl // public/common/oak/oalioctl/oalioctl.cpp
EXTKernelIoCtl // private/winceos/coreos/nk/kernel/kwin32.c

How to implement our own oalioctl
It’s a fair simple task to implement oalioctl layer for our own platform with following steps:

  1. copy public/common/oak/oalioctl directory to platform/platform_name/src/drivers
  2. change TARGETTYPE to DYNLINK in sources file
  3. define our own iocontrol code with CTL_CODE macro
  4. add a case branch for the new iocontrol code

resolve windows ce remote tool connection issue

March 9, 2011

remote tools for windows ce is a set of powerful tools for debugging. I have Visual Studio 2005, Windows Embedded CE 6.0 R3 installed, but the remote tools don’t work. They fail to connect to device with following error message:
The Microsoft ActiveSync reported the following error: Unable to load device side components. Please check server configuration settings.

There are two ways to resolve the connection issue.

1. Run remote tools from windows start menu (e.g., Microsoft Visual Studio 2005\Visual Studio Remote Tools\Remote Process Viewer, which is a shortcut to C:\Program Files\CE Remote Tools\5.01\bin\ccpview.exe), instead of starting from visual studio menu (e.g., Target/Remote Tools/Process Viewer, which is a shortcut to C:\Program Files\Common Files\Microsoft Shared\Windows CE Tools\Platman\bin\wce600\cepview.exe). remote tools version 5.01 work fine.

2. Copy
c:\Program Files\Common Files\Microsoft Shared\Windows CE Tools\Platman\target\wce600\armV4i\
c:\Program Files\Common Files\Microsoft Shared\Windows CE Tools\Platman\target\wce600\armV4\
. The lack of the second directory is a bug in remote tools version 6 that causes the connection issue.

view call stack of crashed application on android

January 26, 2011

On android, when a process crashes in native code, the call stack of the process will be saved to a log file in /data/tombstomes/, and written to logcat as well. The information is helpful for debugging.
Unfortunately, the call stack doesn’t show in human readable format, file name, function name. Instead, it’s shown as module name (e.g., and memory address of the instruction. We can use addr2line to translate the address to corresponding file name and function name if we have the binary of the module that contains symbol information.
To make it easier to use, this function is included in agdb tool (see here for more). We can use “ -r -e module_name address” to find out the function name of specified address within the module.

When we have a long call stack, instead of running the command above for each line in the call stack manually, we can feed the whole call stack to agdb through pipe and get the full resolved call stack. For example, use  “adb logcat | -r” command for adb logcat output with below contents:

22 F/ASessionDescription(   33): frameworks/base/media/libstagefright/rtsp/ASessionDescription.cpp:264 CHECK_GT( end,s) failed:  vs.
23 I/DEBUG   (   30): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
24 I/DEBUG   (   30): Build fingerprint: ‘generic/generic/generic:2.3.1/GINGERBREAD/eng.raymond.20101222.130550:eng/test-keys’
25 I/DEBUG   (   30): pid: 33, tid: 450  >>> /system/bin/mediaserver <<<
26 I/DEBUG   (   30): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr deadbaad
27 I/DEBUG   (   30):  r0 deadbaad  r1 0000000c  r2 00000027  r3 00000000
28 I/DEBUG   (   30):  r4 00000080  r5 afd46668  r6 40806c10  r7 00000000
29 I/DEBUG   (   30):  r8 8031db1d  r9 0000fae0  10 00100000  fp 00000001
30 I/DEBUG   (   30):  ip ffffffff  sp 40806778  lr afd19375  pc afd15ef0  cpsr 00000030
31 I/DEBUG   (   30):          #00  pc 00015ef0  /system/lib/
32 I/DEBUG   (   30):          #01  pc 00001440  /system/lib/
33 I/DEBUG   (   30):
34 I/DEBUG   (   30): code around pc:
35 I/DEBUG   (   30): afd15ed0 68241c23 d1fb2c00 68dae027 d0042a00
36 I/DEBUG   (   30): afd15ee0 20014d18 6028447d 48174790 24802227
37 I/DEBUG   (   30): afd15ef0 f7f57002 2106eb56 ec92f7f6 0563aa01
38 I/DEBUG   (   30): afd15f00 60932100 91016051 1c112006 e818f7f6
39 I/DEBUG   (   30): afd15f10 2200a905 f7f62002 f7f5e824 2106eb42
40 I/DEBUG   (   30):
41 I/DEBUG   (   30): code around lr:
42 I/DEBUG   (   30): afd19354 b0834a0d 589c447b 26009001 686768a5
43 I/DEBUG   (   30): afd19364 220ce008 2b005eab 1c28d003 47889901
44 I/DEBUG   (   30): afd19374 35544306 d5f43f01 2c006824 b003d1ee
45 I/DEBUG   (   30): afd19384 bdf01c30 000281a8 ffffff88 1c0fb5f0
46 I/DEBUG   (   30): afd19394 43551c3d a904b087 1c16ac01 604d9004
47 I/DEBUG   (   30):
48 I/DEBUG   (   30): stack:
49 ……………………
92 I/DEBUG   (   30):     408067e4  6f697470
93 I/BootReceiver(   75): Copying /data/tombstones/tombstone_09 to DropBox (SYSTEM_TOMBSTONE)

we get:

22 F/ASessionDescription(   33): frameworks/base/media/libstagefright/rtsp/ASessionDescription.cpp:264 CHECK_GT( end,s) failed:  vs.
23 I/DEBUG   (   30): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
24 I/DEBUG   (   30): Build fingerprint: ‘generic/generic/generic:2.3.1/GINGERBREAD/eng.raymond.20101222.130550:eng/test-keys’
25 I/DEBUG   (   30): pid: 33, tid: 450  >>> /system/bin/mediaserver <<<
26 I/DEBUG   (   30): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr deadbaad
27 I/DEBUG   (   30):  r0 deadbaad  r1 0000000c  r2 00000027  r3 00000000
28 I/DEBUG   (   30):  r4 00000080  r5 afd46668  r6 40806c10  r7 00000000
29 I/DEBUG   (   30):  r8 8031db1d  r9 0000fae0  10 00100000  fp 00000001
30 I/DEBUG   (   30):  ip ffffffff  sp 40806778  lr afd19375  pc afd15ef0  cpsr 00000030
31 I/DEBUG   (   30):          #00  pc 00015ef0  /system/lib/
32 I/DEBUG   (   30):          #00  __libc_android_abort: abort.c:82
33 I/DEBUG   (   30):          #01  pc 00001440  /system/lib/
34 I/DEBUG   (   30):          #01  __android_log_assert: logd_write.c:235
35 I/DEBUG   (   30):
36 I/DEBUG   (   30): code around pc:
37 I/DEBUG   (   30): afd15ed0 68241c23 d1fb2c00 68dae027 d0042a00
38 I/DEBUG   (   30): afd15ee0 20014d18 6028447d 48174790 24802227
39 I/DEBUG   (   30): afd15ef0 f7f57002 2106eb56 ec92f7f6 0563aa01

Similarly, we copy a tombstone file to our development pc, and use “cat tombstone_01.txt | -r” command to resolve call stack addresses in the tombstone log file.