And note that I can not pass in a ViewController pointer due to this function being passed into another function.
static int callback(void *NotUsed, int argc, char **argv, char **azColName)
{
NSString *str = #"";
int i;
for(i=0; i<argc; i++)
{
printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
str = [NSString stringWithFormat:#"%#\n%s = %s\n", str, azColName[i], argv[i] ? argv[i] : "NULL"];
}
printf("\n");
//tvDisplay is a UITextView
[tvDisplay setText:str]; // <---- ??? how to get to an iVar
return 0;
}
the call:
rc = sqlite3_exec(db, pSQL[i], callback, 0, &zErrMsg);
Callback functions typically have an argument that allows you to pass along arbitrary data (it's usually a void * called context or something similar). You can pass in the object that you need to access when you set up the callback function, and then retrieve it within the callback function:
static void myCallback(int someResult, void *context) {
SomeClass *someObject = (SomeClass *)context;
[someObject doStuff];
}
In your particular case, the place for the "arbitrary data that you want to access in the callback function" is the void * argument right after the callback function itself that you have presently set to 0:
int sqlite3_exec(
sqlite3*, /* An open database */
const char *sql, /* SQL to be evaluated */
int (*callback)(void*,int,char**,char**), /* Callback function */
void *, /* 1st argument to callback */
char **errmsg /* Error msg written here */
);
Keep in mind that you're responsible for ensuring that any data you stick in there remains valid while the callback has not yet returned, and, if necessary, free it in the callback.
Related
I'm using https://github.com/nodejs/http-parser, the callbacks it uses are like this
struct http_parser_settings {
http_cb on_message_begin;
http_data_cb on_url;
http_data_cb on_status;
http_data_cb on_header_field;
http_data_cb on_header_value;
http_cb on_headers_complete;
http_data_cb on_body;
http_cb on_message_complete;
/* When on_chunk_header is called, the current chunk length is stored
* in parser->content_length.
*/
http_cb on_chunk_header;
http_cb on_chunk_complete;
};
The main callback type is defined here
typedef int (*http_data_cb) (http_parser*, const char *at, size_t length);
I'm trying to find a way to pass either an Objective-C block or method as the function pointer in the parser_settings. However it lets me use only a C-function, which doesn't suit me because I also need to access the state of an Objective-C object in the callback
At the moment my solution is as follows:
int onHeaderField(http_parser* _, const char* at, size_t length) {
// Need to access state here, so doesn't work for me as a c function
char header[length];
strncpy(header, at, length);
NSLog(#"Header %s", header);
return 0;
}
...
- (void)method {
http_parser_settings settings;
settings.on_header_field = onHeaderField; // rather than func would like to set a block/method to capture and access self
size_t nparsed = http_parser_execute(self.parser, &parserSettings, charData, messageLength)
}
How would I go about accessing self from the callback passed to http_parser_execute?
Technically you can "extract" an Objective-C method implementation in form of a C-pointer with use of class_getMethodImplementation, however these implementations have objc_msgSend-like signature and always require the receiver as an argument, thus not really usable outside of Objective-C world:
NSString *str = #"Hollow World";
SEL sel = #selector(isEqualToString:);
Method meth = class_getInstanceMethod([str class], sel);
typedef BOOL(*IsEqualToStringPtr)(NSString *, SEL, NSString *);
IsEqualToStringPtr impl = (IsEqualToStringPtr)method_getImplementation(meth);
NSLog(#"Is equal? %#", impl(str, sel, #"Hello, World!") ? #"YES" : #"NO"); // prints "NO"
NSLog(#"Is equal? %#", impl(str, sel, #"Hollow World") ? #"YES" : #"NO"); // prints "YES"
Having that said, neither blocks nor Objective-C methods are directly convertible to a C function pointer (they are pointers to structures under the hood), especially when you want to complement it with any kind of context/state.
The simplest thing you can do is to use a global/statically allocated block variable which can be accessed from a C function without altering it's signature:
static int(^StaticBlock)(http_parser *parser, const char *at, size_t length);
static int my_callback(http_parser *parser, const char *at, size_t length) {
return StaticBlock(parser, at, length);
}
...
- (void)someObjectiveCMethod {
__weak typeof(self) weakSelf = self;
StaticBlock = ^(http_parser *parser, const char *at, size_t length) {
if (!weakSelf) {
return -1;
}
__strong typeof(weakSelf) strongSelf = weakSelf;
strongSelf.mprpty += length;
NSLog(#"Hello from Objective-C");
return 8;
};
http_parser_settings settings;
settings.on_header_field = my_callback;
}
The only viable alternative I can think of is using C++ lambdas. However it's still a big challenge when you need to access current state/context, let alone it will require you to switch to Objective-C++. If you are ok with it, first you need to rename your Objective-C file from SomeClass.m into SomeClass.mm. This way you tell Clang that the source code is Objective-C++ now and the compiler should accept a C++ code. Next, if your C library doesn't have C++ guards, you may want to wrap the C includes with extern "C" expression (otherwise linker would not be able to locate C symbols, because C++ mangles them):
extern "C" {
#include <c_header.h>
}
Now the tricky part: lambda expressions return special objects, closures, which can be seamlessly converted to C function pointers only if they don't capture anything from surrounding context. In our scenario it's not the case and it will require extra steps to convert it to a C pointer. Add this code somewhere in your *.mm file:
template<typename L>
struct c_functor_factory : c_functor_factory<decltype(&L::operator())> {};
template<typename R, typename F, typename ...Args>
struct c_functor_factory<R(F::*)(Args...) const> {
using pointer = typename std::add_pointer<R(Args...)>::type;
static pointer make_cptr(F&& func) {
static F instance = std::forward<F>(func);
return [](Args... args) {
return instance(std::forward<Args>(args)...);
};
}
};
template<typename L>
inline static typename c_functor_factory<L>::pointer make_cptr(L&& lambda) {
return c_functor_factory<L>::make_cptr(std::forward<L>(lambda));
}
In fact this solution is not much far from the global C function solution I suggested above. When a closure is passed as an argument here, this template function just perfect-forwards it to a statically allocated variable. As a result the static closure can be called from a capture-less lambda, which in turn is converted to a C function pointer.
Finally, you can make use of C++ lambda expressions and pass them as C function pointers anywhere in your Objective-C code:
- (void)someObjectiveCMethod {
__weak typeof(self) weakSelf = self;
const auto cptr = make_cptr([weakSelf](http_parser *parser, const char *at, size_t length) {
if (!weakSelf) {
return -1;
}
__strong typeof(weakSelf) strongSelf = weakSelf;
strongSelf.num += val;
NSLog(#"Hello from Objective-C++, %s!", at);
return 32;
});
http_parser_settings settings;
settings.on_header_field = my_callback;
}
Unlike the previous one, C++ solution is much more reliable, because each time your code hits the lambda expression, it emits a new closure object. In both cases, however, the function objects have static storage duration, thus make sure you don't pass any strong pointer in the body of it (otherwise it will never be released).
I've been working on making an app with kivy/python and I needed to call some ios frameworks with obj-c. So I've made a couple layers of wrappers with python->cython->c->obj-c->framework. So far I've got everything to work up until the call back funtion that goes all the way back through to python. Right now the call back is failing somewhere between the cython->C->obj-c layer (never hits my print in cython). I feel like its because I'm trying to call user_func as a C function and not like an obj-c function. How should I go about running my C callback func inside of obj-c? I've peppered the code with prints (can't step through the way my setup is) and it prints the token that's generated and then crashes right on the user_func. It also never reaches the callback function in my cython file. So somewhere between the two is the source of the crash.
- (void) retrieveTokenObjC:(char*)myKey andcardNumber:(char*)cardNumber andexpMonth:(int)expMonth andexpYear:(int)expYear andcvc:(char*)cvc anduser_func:(tokenfunc)user_func anduser_data:(void*)user_data {
NSString* NScardNumber = [NSString stringWithUTF8String:cardNumber];
NSString* NScvc = [NSString stringWithUTF8String:cvc];
STPCardParams *cardParams = [[STPCardParams alloc] init];
cardParams.number = NScardNumber;
cardParams.expMonth = expMonth;
cardParams.expYear = expYear;
cardParams.cvc = NScvc;
NSString *myPublishableKey = [NSString stringWithUTF8String:myKey];
STPAPIClient *apiClient = [[STPAPIClient alloc] initWithPublishableKey:myPublishableKey];
[apiClient createTokenWithCard:cardParams completion:^(STPToken *token,NSError *error) {
if (token == nil || error != nil) {
const char* errorChar = [error.localizedDescription UTF8String];
user_func(errorChar,user_data);
} else {
const char* tokenChar = [token.tokenId UTF8String];
user_func(tokenChar,user_data);
}
}];
}
After this it goes the obj-c header
#import <Foundation/Foundation.h>
typedef void (*tokenfunc) (const char *name, void *user_data);
#interface retToken : NSObject
- (void) retrieveTokenObjC:(char*)myKey andcardNumber:(char*)cardNumber andexpMonth:(int)expMonth andexpYear:(int)expYear andcvc:(char*)cvc anduser_func:(tokenfunc)user_func anduser_data:(void*)user_data;
#end
Then it goes into a c wrapper for cython.
#include "stripe_ios_c.h"
#include "stripe_ios_imp.h"
void retrieveToken(char* myKey, char* cardNumber, int expMonth, int expYear, char* cvc,tokenfunc user_func, void *user_data){
retToken* retrieveToken = [[retToken alloc] init];
[retrieveToken retrieveTokenObjC:myKey andcardNumber:cardNumber andexpMonth:expMonth andexpYear:expYear andcvc:cvc anduser_func:user_func anduser_data:user_data];
}
Then the header file for the c wrapper
typedef void (*tokenfunc)(const char *name, void *user_data);
void retrieveToken(char* myKey, char* cardNumber, int expMonth, int expYear, char* cvc,tokenfunc user_func, void *user_data);
And finally to the cython code
__all__ = ['StripeWrapper']
cdef extern from "stripe_ios_c.h":
ctypedef void (*tokenfunc)(const char *name, void *user_data)
void retrieveToken(char* myKey, char* cardNumber, int expMonth, int expYear, char* cvc,tokenfunc user_func, void *user_data)
class StripeWrapper():
def __init__(self,**kwargs):
foo = 'bar'
pass
def getToken(self,tokenCallback,myKey,cardNumber,expMonth,expYear,cvc):
cdef bytes myKey_bytes = myKey.encode('utf-8')
cdef char* myKey_string = myKey_bytes
cdef bytes cardNumber_bytes = cardNumber.encode('utf-8')
cdef char* cardNumber_string = cardNumber_bytes
cdef bytes cvc_bytes = cvc.encode('utf-8')
cdef char* cvc_string = cvc_bytes
print myKey_bytes
print cardNumber_bytes
print cvc_bytes
print myKey_string
print cardNumber_string
print cvc_string
retrieveToken(myKey_bytes, cardNumber_bytes, expMonth, expYear, cvc_bytes, callback, <void*>tokenCallback)
print 'Debug 1'
cdef void callback(const char *name, void *tokenCallback):
print 'callback debug'
(<object>tokenCallback)(name.decode('utf-8'))
Update: I've tracked the issue down and my call back function executes the problem is the python callback is being deallocated somewhere along the way.
I solved the issue. The example here https://github.com/cython/cython/blob/master/Demos/callback/run_cheese.py for a cython callback won't work if you leave the main/current file. This is because the moment you leave that file the memory is deallocated. After pushing a python object and using
cdef void callback(const char *name, void *tokenCallback):
(<object> tokenCallback).token = (name.decode('utf-8'))
I feel like the cython is example is kind of a bad example and should have used an object to send the callback with which could have prevented lots of frustration but it finally works!
I get strange code errors when I rename the following command line program from main.m to main.mm. Works just fine as main.m. Anyone know why?
https://stackoverflow.com/a/36469891/105539
SOURCE
#import <Foundation/Foundation.h>
void detectNewFile (
ConstFSEventStreamRef streamRef,
void *clientCallBackInfo,
size_t numEvents,
void *eventPaths,
const FSEventStreamEventFlags eventFlags[],
const FSEventStreamEventId eventIds[])
{
int i;
char **paths = eventPaths;
printf("GOT AN EVENT!!!!\n");
for (i=0; i<numEvents; i++) {
printf("Change %llu in %s, flags %u\n", eventIds[i], paths[i], (unsigned int)eventFlags[i]);
}
}
int main(int argc, const char * argv[]) {
#autoreleasepool {
short nPathCount = 2;
CFStringRef mypath[nPathCount];
mypath[0] = CFSTR("/Users/mike/Documents");
mypath[1] = CFSTR("/Users/mike/Downloads");
CFArrayRef pathsToWatch = CFArrayCreate(NULL, (const void **)&mypath, nPathCount, NULL);
void *callbackInfo = NULL;
CFAbsoluteTime latency = 1.0; // seconds
FSEventStreamRef hStream = FSEventStreamCreate(NULL,
&detectNewFile,
callbackInfo,
pathsToWatch,
kFSEventStreamEventIdSinceNow,
latency,
kFSEventStreamCreateFlagFileEvents
);
FSEventStreamScheduleWithRunLoop(hStream, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode);
FSEventStreamStart(hStream);
printf("Waiting on new file creations...\n");
CFRunLoopRun(); // runs in an endless loop, only letting the callback function run
} // end autorelease pool
return 0;
}
ERRORS
FOR:
char **paths = eventPaths;
Cannot initialize a variable of type 'char **' with an lvalue of type 'void *'
FOR:
FSEventStreamRef hStream = FSEventStreamCreate(NULL,
&detectNewFile,
callbackInfo,
pathsToWatch,
kFSEventStreamEventIdSinceNow,
latency,
kFSEventStreamCreateFlagFileEvents
);
No matching function for call to 'FSEventStreamCreate'
Thanks to #johnelemans, I found the problems. In C, it's legal to have automatic casting from void * to char **, but not in C++, which is what the .mm file would switch this into. The fix is to use casting:
char **paths = (char **)eventPaths;
Then, on the FSEventStreamCreate, it didn't like the void * instead of this:
FSEventStreamContext *callbackInfo = NULL;
...and didn't like the CFAbsoluteTime instead of:
CFTimeInterval latency = 1.0; // seconds
Then, you need to add CoreServices.framework library to the build steps.
I made those changes and it compiles now.
I'm trying to create my own custom assert. However, I would like my assertion to automatically include all of the relevant variables. This seems really basic to me, and I've searched around for about an hour but I can't seem to find a way get access to all the relevant stack frame variables. Does anyone know how to get these variables?
FYI - I don't need to access the variables in the debugger, I need to access them programmatically. I would like to upload them along with the crash report to give me more information about the crash. I also know that I can print them out manually...that is exactly what I'm looking to avoid.
You are basically asking to re-invent a good sized chunk of the debugger.
Without symbols, there isn't anything you can interrogate to figure out the layout of the local frame. Even with symbols, it is quite likely that the optimizer will have stomped on any local variables as the optimizer will re-use stack slots at whim once it determines the variable is no longer needed within the frame.
Note that many crashes won't be able to be caught at all or, if caught, the frame within which they occurred will have long since been destroyed.
Since you mention that you are creating a custom assertion, it sounds like you really aren't looking to introspect crashes as much as dump a snap of the local frame when you programatically detect that things have gone off the rails. While there really isn't a means of automatically reporting on local stack state, you could do something like:
{ ... some function ....
... local variables ...
#define reportblock ^{ ... code that summarizes locals ... ; return summary; }
YourAssert( cond, "cond gone bad. summary: %#", reportblock());
}
Note that the #define ensures that each YourAssert() captures the state at the time of the assertion. Note also that the above might have a potentially significant impact on performance.
Note also that I just made that code up. It seems like it is worthy of investigation, but may prove non-viable for a number of reasons.
If you're willing to use Objective-C++, then this is definitely a possibility, as long as you are also willing to declare your variables differently, and understand that you will only be able to grab your own variables with this method.
Also note that it will increase your stack frame size with extra __stack_ variables, which could cause memory issues (although I doubt it, personally).
It won't work with certain constructs such as for-loops, but for 95% of cases, this should work for what you need:
#include <vector>
struct stack_variable;
static std::vector<const stack_variable *> stack_variables;
struct stack_variable {
void **_value;
const char *_name;
const char *_type;
const char *_file;
const char *_line;
private:
template<typename T>
stack_variable(const T& value, const char *type, const char *name, const char *file, const char *line) : _value((void **) &value), _type(type), _name(name), _file(file), _line(line) {
add(*this);
}
static inline void add(const stack_variable &var) {
stack_variables.push_back(static_cast<const stack_variable *>(&var));
}
static inline void remove(const stack_variable &var) {
for (auto it = stack_variables.begin(); it != stack_variables.end(); it++) {
if ((*it) == &var) {
stack_variables.erase(it);
return;
}
}
}
public:
template<typename T>
static inline stack_variable create(const T& value, const char *type, const char *name, const char *file, const char *line) {
return stack_variable(value, type, name, file, line);
}
~stack_variable() {
remove(*this);
}
void print() const {
// treat the value as a pointer
printf("%s:%s - %s %s = %p\n", _file, _line, _type, _name, *_value);
}
static void dump_vars() {
for (auto var : stack_variables) {
var->print();
}
}
};
#define __LINE_STR(LINE) #LINE
#define _LINE_STR(LINE) __LINE_STR(LINE)
#define LINE_STR _LINE_STR(__LINE__)
#define LOCAL_VAR(type, name, value)\
type name = value;\
stack_variable __stack_ ## name = stack_variable::create<type>(name, #type, #name, __FILE__, LINE_STR);\
(void) __stack_ ## name;
Example:
int temp() {
LOCAL_VAR(int, i_wont_show, 0);
return i_wont_show;
}
int main(){
LOCAL_VAR(long, l, 15);
LOCAL_VAR(int, x, 192);
LOCAL_VAR(short, y, 256);
temp();
l += 10;
stack_variable::dump_vars();
}
Output (note the junk extra bytes for the values smaller than sizeof(void *), there isn't much I can do about that):
/Users/rross/Documents/TestProj/TestProj/main.mm:672 - long l = 0x19
/Users/rross/Documents/TestProj/TestProj/main.mm:673 - int x = 0x5fbff8b8000000c0
/Users/rross/Documents/TestProj/TestProj/main.mm:674 - short y = 0xd000000010100
Threads will royally screw this up, however, so in a multithreaded environment this is (almost) worthless.
I decided to add this as a separate answer, as it uses the same approach as my other one, but this time with an all ObjC code. Unfortunately, you still have to re-declare all of your stack variables, just like before, but hopefully now it will work better with your existing code-base.
StackVariable.h:
#import <Foundation/Foundation.h>
#define LOCAL_VAR(p_type, p_name, p_value)\
p_type p_name = p_value;\
StackVariable *__stack_ ## p_name = [[StackVariable alloc] initWithPointer:&p_name\
size:sizeof(p_type)\
name:#p_name\
type:#p_type\
file:__FILE__\
line:__LINE__];\
(void) __stack_ ## p_name;
#interface StackVariable : NSObject
-(id) initWithPointer:(void *) ptr
size:(size_t) size
name:(const char *) name
type:(const char *) type
file:(const char *) file
line:(const int) line;
+(NSString *) dump;
#end
StackVariable.m:
#import "StackVariable.h"
static NSMutableArray *stackVariables;
#implementation StackVariable {
void *_ptr;
size_t _size;
const char *_name;
const char *_type;
const char *_file;
int _line;
}
-(id) initWithPointer:(void *)ptr size:(size_t)size name:(const char *)name type:(const char *)type file:(const char *)file line:(int)line
{
if (self = [super init]) {
if (stackVariables == nil) {
stackVariables = [NSMutableArray new];
}
_ptr = ptr;
_size = size;
_name = name;
_type = type;
_file = file;
_line = line;
[stackVariables addObject:[NSValue valueWithNonretainedObject:self]];
}
return self;
}
-(NSString *) description {
NSMutableString *result = [NSMutableString stringWithFormat:#"%s:%d - %s %s = { ", _file, _line, _type, _name];
const uint8_t *bytes = (const uint8 *) _ptr;
for (size_t i = 0; i < _size; i++) {
[result appendFormat:#"%02x ", bytes[i]];
}
[result appendString:#"}"];
return result;
}
+(NSString *) dump {
NSMutableString *result = [NSMutableString new];
for (NSValue *value in stackVariables) {
__weak StackVariable *var = [value nonretainedObjectValue];
[result appendString:[var description]];
[result appendString:#"\n"];
}
return result;
}
-(void) dealloc {
[stackVariables removeObject:[NSValue valueWithNonretainedObject:self]];
}
#end
Example:
#include "StackVariable.h"
int temp() {
LOCAL_VAR(int, i_wont_show, 0);
return i_wont_show;
}
int main(){
LOCAL_VAR(long, l, 15);
LOCAL_VAR(int, x, 192);
LOCAL_VAR(short, y, 256);
temp();
l += 10;
puts([[StackVariable dump] UTF8String]);
}
Output:
/Users/rross/Documents/TestProj/TestProj/main.m:676 - long l = { 19 00 00 00 00 00 00 00 }
/Users/rross/Documents/TestProj/TestProj/main.m:677 - int x = { c0 00 00 00 }
/Users/rross/Documents/TestProj/TestProj/main.m:678 - short y = { 00 01 }
This requires ARC (and all of it's magic) enabled for any file you want to test this in, or you will manually have to release the __stack_ variables, which won't be pretty.
However, it now gives you a hex dump of the variable (rather than the weird pointer one), and if you really tried hard enough (using __builtin_types_compatible), it could detect whether the result was an object, and print that.
Once again, threads will mess this up, but a simple way to fix that would be to create a NSDictionary of NSArrays, with a NSThread as the key. Makes it a bit slower, but let's be honest, if you're using this over the C++ version, you aren't going for performance.
Block variable in objective-c is a reference and I learned from somewhere infer that following code may be transformed by compiler to another form.
Original code:
typedef int (^block_type)();
block_type create_k(int i)
{
block_type block = ^(){
return i;
};
//[block copy];
return block;
}
Generated Code:
typedef void (*generic_invoke_funcptr)(void *, ...);
struct __block_literal {
void *isa;
int flags;
int reserved;
generic_invoke_funcptr invoke;
struct __block_descriptor_tmp *descriptor;
const int captured_i;
};
static const struct __block_descriptor_tmp {
unsigned long reserved;
unsigned long literal_size;
/* no copy/dispose helpers needed */
} __block_descriptor_tmp = {
0UL, sizeof(struct __block_literal)
};
// ^int (void) { return i; }
int __create_k_block_invoke_(struct __block_literal *bp) {
return bp->captured_i;
}
typedef int (*iv_funcptr)(struct __block_literal *);
typedef int (^block_type)();
block_type create_k(int i)
{
//block_type block = ^(){
// return i;
//};
struct __block_literal __b = {
.isa = &_NSConcreteStackBlock,
.flags = BLOCK_HAS_DESCRIPTOR,
.reserved = 0,
.invoke = (generic_invoke_funcptr)__f_block_invoke_,
.descriptor = &__block_descriptor_tmp,
.captured_i = i
};
struct __block_literal *block = &__b;
return block;
}
So |_b| in stack and block is only a reference to |_b|. If |create_k| return |block|, the receiver only get a invalid address.
But
int main(int argc, const char *argv[])
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
printf("%d\n", create_k(40)());
[pool drain];
return 0;
}
By exec it, print |40| and |block| is a valid block. What's the matter?
My guess would be that the memory for that stack frame hasn't been zeroed yet. Try calling another function between create_k() and printf() to get some other random data in there.