This must be very simple, but I can't figure out how to do this: I have a C-function to monitor current memory usage:
natural_t report_memory(void) {
struct task_basic_info info;
mach_msg_type_number_t size = sizeof(info);
kern_return_t kerr = task_info(mach_task_self(),
TASK_BASIC_INFO,
(task_info_t)&info,
&size);
if( kerr == KERN_SUCCESS ) {
return info.resident_size;
} else {
NSLog(#"Error with task_info(): %s", mach_error_string(kerr));
return 0;
}
}
Now, I would like to use it. How do I declare it in the .h?
I tried the (for me) obvious within the objective c methods:
natural_t report_memory(void);
Calling this somewhere in the code:
NSLog(#"Memory used: %u", rvC.report_memory());
The Compiler complains error: called object is not a function. Thus, I assume, the declaration is somehow wrong. I tried several options, but the best I could get was a runtime error...
How to fix this?
rvC.report_memory()
should be replaced with
report_memory()
since it is a C function.
If you want to use this function in other modules, you should also put in your header (.h) file this line
extern natural_t report_memory(void);
Related
I am creating a currency converter Win32 program in Embarcadero C++Builder. I wrote a function for transforming date from format specified on user PC to YYYY-MM-DD format. I need that part because of API settings.
When I have this function inside my project it works fine, but I need to have that function inside a DLL.
This is how my code looks like:
#pragma hdrstop
#pragma argsused
#include <SysUtils.hpp>
extern DELPHI_PACKAGE void __fastcall DecodeDate(const System::TDateTime DateTime, System::Word &Year, System::Word &Month, System::Word &Day);
extern "C" UnicodeString __declspec (dllexport) __stdcall datum(TDateTime dat) {
Word dan, mjesec, godina;
UnicodeString datum, datum_dan, datum_mjesec, datum_godina;
DecodeDate(dat, godina, mjesec, dan);
if (dan<=9 && mjesec<=9) {
datum_dan="0"+IntToStr(dan);
datum_mjesec="0"+IntToStr(mjesec);
}
if (dan<=9 && mjesec>9) {
datum_dan="0"+IntToStr(dan);
datum_mjesec=IntToStr(mjesec);
}
if (dan>9 && mjesec<=9) {
datum_dan=IntToStr(dan);
datum_mjesec="0"+IntToStr(mjesec);
}
if (dan>9 && mjesec>9) {
datum_dan=IntToStr(dan);
datum_mjesec=IntToStr(mjesec);
}
datum_godina=IntToStr(godina);
return datum_godina+"-"+datum_mjesec+"-"+datum_dan;
}
extern "C" int _libmain(unsigned long reason)
{
return 1;
}
`
I've included SysUtils.hpp and declared DecodeDate() function, without those lines I have a million errors. But with code looking like this, I am getting this error, which I can't get rid of:
[bcc32 Error] File1.cpp(30): E2015 Ambiguity between '_fastcall System::Sysutils::DecodeDate(const System::TDateTime,unsigned short &,unsigned short &,unsigned short &) at c:\program files (x86)\embarcadero\studio\19.0\include\windows\rtl\System.SysUtils.hpp:3466' and '_fastcall DecodeDate(const System::TDateTime,unsigned short &,unsigned short &,unsigned short &) at File1.cpp:25'
Full parser context
File1.cpp(27): parsing: System::UnicodeString __stdcall datum(System::TDateTime)
Can you help me to get rid of that error?
The error message is self-explanatory. You have two functions with the same name in scope, and the compiler doesn't know which one you want to use on line 30 because the parameters you are passing in satisfy both function declarations.
To fix the error, you can change this line:
DecodeDate(dat, godina, mjesec, dan);
To either this:
System::Sysutils::DecodeDate(dat, godina, mjesec, dan);
Or this:
dat.DecodeDate(&godina, &mjesec, &dan);
However, either way, you should get rid of your extern declaration for DecodeDate(), as it doesn't belong in this code at all. You are not implementing DecodeDate() yourself, you are just using the one provided by the RTL. There is already a declaration for DecodeDate() in SysUtils.hpp, which you are #include'ing in your code. That is all the compiler needs.
Just make sure you are linking to the RTL/VCL libraries to resolve the function during the linker stage after compiling. You should have enabled VCL support when you created the DLL project. If you didn't, recreate your project and enable it.
BTW, there is a MUCH easier way to implement your function logic - instead of manually pulling apart the TDateTime and reconstituting its components, just use the SysUtils::FormatDateTime() function or the TDateTime::FormatString() method instead, eg:
UnicodeString __stdcall datum(TDateTime dat)
{
return FormatDateTime(_D("yyyy'-'mm'-'dd"), dat);
}
UnicodeString __stdcall datum(TDateTime dat)
{
return dat.FormatString(_D("yyyy'-'mm'-'dd"));
}
That being said, this code is still wrong, because it is not safe to pass non-POD types, like UnicodeString, over the DLL boundary like you are doing. You need to re-think your DLL function design to use only interop-safe POD types. In this case, change your function to either:
take a wchar_t* as input from the caller, and just fill in the memory block with the desired characters. Let the caller allocate the actual buffer and pass it in to your DLL for populating:
#pragma hdrstop
#pragma argsused
#include <SysUtils.hpp>
extern "C" __declspec(dllexport) int __stdcall datum(double dat, wchar_t *buffer, int buflen)
{
UnicodeString s = FormatDateTime(_D("yyyy'-'mm'-'dd"), dat);
if (!buffer) return s.Length() + 1;
StrLCopy(buffer, s.c_str(), buflen-1);
return StrLen(buffer);
}
extern "C" int _libmain(unsigned long reason)
{
return 1;
}
wchar_t buffer[12] = {};
datum(SomeDateValueHere, buffer, 12);
// use buffer as needed...
int len = datum(SomeDateValueHere, NULL, 0);
wchar_t *buffer = new wchar_t[len];
int len = datum(SomeDateValueHere, buffer, len);
// use buffer as needed...
delete[] buffer;
allocate a wchar_t[] buffer to hold the desired characters, and then return a wchar_t* pointer to that buffer to the caller. Then export a second function that the caller can pass the returned wchar_t* back to you so you can free it correctly.
#pragma hdrstop
#pragma argsused
#include <SysUtils.hpp>
extern "C" __declspec(dllexport) wchar_t* __stdcall datum(double dat)
{
UnicodeString s = FormatDateTime("yyyy'-'mm'-'dd", dat);
wchar_t* buffer = new wchar_t[s.Length()+1];
StrLCopy(buffer, s.c_str(), s.Length());
return buffer;
}
extern "C" __declspec(dllexport) void __stdcall free_datum(wchar_t *dat)
{
delete[] dat;
}
extern "C" int _libmain(unsigned long reason)
{
return 1;
}
wchar_t *buffer = datum(SomeDateValueHere);
// use buffer as needed...
free_datum(buffer);
I want the address of an objective-C function to equal a pointer to a C function
I can get it to work with the following C function but i would like to use only objective-C if possible
//member function from type pjsua_callback (cfg.cb)
void(* on_call_state )(pjsua_call_id call_id, pjsip_event *e)
//Initialize the applications configuration callbacks
app_config->cfg.cb.on_call_state = &on_call_state;
.
// Callback called by the library when call's state has changed
void on_call_state(pjsua_call_id call_id, pjsip_event *e) {
NSLog(#"on_call_state, call_id = %d", call_id);
pjsua_call_info ci;
pjsua_call_get_info(call_id, &ci);
postCallStateNotification(call_id, &ci);
}
I want to achieve this using an objective-c function
//objective-c function attempting to recreate the c function
- (void)on_call_state:(pjsua_call_id )call_id andEvent:(pjsip_event *)e{
NSLog(#"on_call_state, call_id = %d", call_id);
pjsua_call_info ci;
pjsua_call_get_info(call_id, &ci);
[self postCallStateNotification:call_id andCallInfo:&ci];
}
Why can't I get the objective-c function to return (void) like the c function and initialize the callback like so (without arguments like in the c function)
cfg.cb.on_call_state = &[self on_call_state:andEvent:];
i want the cfg.cb.on_call_state to equal the address of my objective-c function
At last I found the solution for this from my own question. For them who are still wondering for the solution, the solution is to make your own C file holding the logic of the callbacks and add your c file into your objective-C code.
So your C file (header file) will look like this
//
// my_app.h
// AnuranRealSIPOBJ
//
// Created by Anuran Barman on 01/07/19.
// Copyright © 2019 Anuran Barman. All rights reserved.
//
#ifndef my_app_h
#define my_app_h
#include <stdio.h>
#import <pjsua.h>
#define THIS_FILE "APP"
static void on_incoming_call(pjsua_acc_id acc_id, pjsua_call_id call_id,
pjsip_rx_data *rdata) {
pjsua_call_info ci;
PJ_UNUSED_ARG(acc_id);
PJ_UNUSED_ARG(rdata);
pjsua_call_get_info(call_id, &ci);
PJ_LOG(3,(THIS_FILE, "Incoming call from %.*s!!",
(int)ci.remote_info.slen,
ci.remote_info.ptr));
/* Automatically answer incoming calls with 200/OK */
pjsua_call_answer(call_id, 200, NULL, NULL);
}
/* Callback called by the library when call's state has changed */
static void on_call_state(pjsua_call_id call_id, pjsip_event *e)
{
pjsua_call_info ci;
PJ_UNUSED_ARG(e);
pjsua_call_get_info(call_id, &ci);
PJ_LOG(3,(THIS_FILE, "Call %d state=%.*s", call_id,
(int)ci.state_text.slen,
ci.state_text.ptr));
}
/* Callback called by the library when call's media state has changed */
static void on_call_media_state(pjsua_call_id call_id)
{
pjsua_call_info ci;
pjsua_call_get_info(call_id, &ci);
if (ci.media_status == PJSUA_CALL_MEDIA_ACTIVE) {
// When media is active, connect call to sound device.
pjsua_conf_connect(ci.conf_slot, 0);
pjsua_conf_connect(0, ci.conf_slot);
}
}
#endif /* my_app_h */
After this just add this line where you are configuring your pjsip user agent in your Objective C code which is expecting the pointer to the function:
#import "my_app.h"
ua_cfg.cb.on_incoming_call = &on_incoming_call;
ua_cfg.cb.on_call_state = &on_call_state;
ua_cfg.cb.on_call_media_state = &on_call_media_state;
Take a look at this C++ code:
#include <iostream>
using namespace std;
class B{
public:
int& f() {
int local_n = 447;
return local_n ;
} // local_n gets out of scope here
};
int main()
{
B b;
int n = b.f(); // and now n = 447
}
I don't understand why n = 447 at the end of main, because I tried to return a reference to a local_n, when it should be NULL;
Returning a reference to a local variable invokes undefined behavior - meaning you might get lucky and it might work... sometimes... or it might format your hard drive or summon nasal demons. In this case, the compiler generated code that managed to copy the old value off the stack before it got overwritten with something else. Oh, and references do not have a corresponding NULL value...
Edit - here's an example where returning a reference is a bad thing. In your example above, since you copy the value out of the reference immediately before calling anything else, it's quite possible (but far from guaranteed) that it might work most of the time. However, if you bind another reference to the returned reference, things won't look so good:
extern void call_some_other_functions();
extern void lucky();
extern void oops();
int& foo()
{ int bar = 0;
return bar;
}
main()
{ int& x = foo();
x = 5;
call_some_other_functions();
if (x == 5)
lucky();
else
oops();
}
Can I declare a C function with an undetermined return type (without C compiler warning)? The return type could be int, float, double, void *, etc.
undetermined_return_type miscellaneousFunction(undetermined_return_type inputValue);
And you can use this function in other functions to return a value (although that could be a run time error):
BOOL isHappy(int feel){
return miscellaneousFunction(feel);
};
float percentage(float sales){
return miscellaneousFunction(sales);
};
What I'm looking for:
To declare and to implement a C function (or Obj-C method) with an undefined-return-type could be useful for aspect-oriented programming.
If I could intercept Obj-C messages in another function in run time, I might return the value of that message to the original receiver or not with doing something else action. For example:
- (unknown_return_type) interceptMessage:(unknown_return_type retValOfMessage){
// I may print the value here
// No idea how to print the retValOfMessage (I mark the code with %???)
print ("The message has been intercepted, and the return value of the message is %???", retValOfMessage);
// Or do something you want (e.g. lock/unlock, database open/close, and so on).
// And you might modify the retValOfMessage before returning.
return retValOfMessage;
}
So I can intercept the original message with a little addition:
// Original Method
- (int) isHappy{
return [self calculateHowHappyNow];
}
// With Interception
- (int) isHappy{
// This would print the information on the console.
return [self interceptMessage:[self calculateHowHappyNow]];
}
You can use a void * type.
Then for example:
float percentage(float sales){
return *(float *) miscellaneousFunction(sales);
}
Be sure not to return a pointer to a object with automatic storage duration.
You may use the preprocessor.
#include <stdio.h>
#define FUNC(return_type, name, arg) \
return_type name(return_type arg) \
{ \
return miscellaneousFunction(arg); \
}
FUNC(float, undefined_return_func, arg)
int main(int argc, char *argv[])
{
printf("\n %f \n", undefined_return_func(3.14159));
return 0;
}
May be a union as suggested by thejh
typedef struct
{
enum {
INT,
FLOAT,
DOUBLE
} ret_type;
union
{
double d;
float f;
int i;
} ret_val;
} any_type;
any_type miscellaneousFunction(any_type inputValue) {/*return inputValue;*/}
any_type isHappy(any_type feel){
return miscellaneousFunction(feel);
}
any_type percentage(any_type sales){
return miscellaneousFunction(sales);
}
Here with ret_type you can know data type of return value and ret_type. i,f,d can give you corresponding value.
All elements will use same memory space and only one should be accessed.
Straight C doesn't support dynamically-typed variables (variants) since it is statically typed, but there might be some libraries that do what you want.
how to pass multiple arguments in a single function in Objective-C? I want to pass 2 integer values and the return value is also integer. I want to use the new Objective-C syntax, not the old C/C++ syntax.
In objective-c it is really super easy. Here is the way you would do it in C:
int functName(int arg1, int arg2)
{
// Do something crazy!
return someInt;
}
This still works in objective-c because of it's compatibility with C, but the objective-c way to do it is:
// Somewhere in your method declarations:
- (int)methodName:(int)arg1 withArg2:(int)arg2
{
// Do something crazy!
return someInt;
}
// To pass those arguments to the method in your program somewhere:
[objectWithOurMethod methodName:int1 withArg2:int2];
Best of luck!
Since this is still google-able and there are better solutions than the accepted answer; there's no need for the hideous withArg2 – just use colons:
Declaration:
#interface
-(void) setValues: (int)v1 : (int)v2;
Definition:
#implementation
-(void) setValues: (int)v1 : (int)v2 {
//do something with v1 and v2
}
Like this:
int sum(int a, int b) {
return a + b;
}
Called like this:
int result;
result = sum(3, 5);
// result is now 8
More here
int add (int a, int b)
{
int c;
c = a + b;
return c;
}
link text