Please tell me what is the difference of
typedef struct Tcl_ObjType {
char *name;
Tcl_FreeInternalRepProc *freeIntRepProc;
Tcl_DupInternalRepProc *dupIntRepProc;
Tcl_UpdateStringProc *updateStringProc;
Tcl_SetFromAnyProc *setFromAnyProc;
} Tcl_ObjType;
and
struct Tcl_ObjType {
char *name;
Tcl_FreeInternalRepProc *freeIntRepProc;
Tcl_DupInternalRepProc *dupIntRepProc;
Tcl_UpdateStringProc *updateStringProc;
Tcl_SetFromAnyProc *setFromAnyProc;
};
I have see the first version here: http://www.tcl.tk/man/tcl8.5/TclLib/ObjectType.htm , and don't know why it is written as it is.
For C++, there is no difference.
If this was a C program and you used the first variant, you could do:
Tcl_ObjType instanceOfStructure;
instead of
struct Tcl_ObjType instanceOfStructure;
You've gave the structure a type definition (In layman terms, provided an alternate name to an existing type):
Using your first example, you can then use it to reference objects/declare new objects via:
Tcl_ObjType newObj;
Related
I have been looking everywhere for this question, but I cannot seem to get the answer for this.
So, every example I have been to is simply how to grab function pointers from SO file, which I have done. However, let just say I have this compiled as my .SO file:
(these codes compiled into libsampleso.so):
sampleso.hpp:
#IFNDEF SAMPLESO_HPP__
#DEFINE SAMPLESO_HPP__
struct carDescriptor
{
const char* model;
int prod_year;
int wheel_num;
const char* license_plate;
const char* colour;
} car;
carDescriptor fillCarID(void);
#ENDIF
sampleso.cpp:
#include "sampleso.hpp"
//Struct car fillup function
carDescriptor fillCarID(void)
{
car.model = "Ford Fiesta";
car.prod_year = 2014;
car.wheel_num = 4;
car.colour = "Midnight Blue";
car.license_plate = "D 1234 ABC";
return car;
}
now, compiled, I've got these out of objdump -T libsampleso.so: car (the struct) and _Z9fillCarIDv (the function).
if the return value of _Z9fillCarIDv() (aka fillCarID()) is normal datatype (e.g. string or int), it's easy with dlsym. However, for this I need to cast the struct first and then the function. I've tried creating an empty struct, and then cast dlsym to it:
struct carDesc * cars;
cars = reinterpret_cast<struct carDesc*>(dlsym(hHandler,"car"));
but seems to be impossible to use that as the datatype for the function:
carDesc(*__fn_fillCarIDv)(void);
__fn_fillCarIDv = reinterpret_cast<carDesc(*)(void)>(dlsym(hHandler,"_Z9fillCarIDv"));
cars = __fn_fillCarIDv(); //doesn't work, error: function returns incomplete type "carDesc" C/C++(862)
Anyone ever tried to grab a struct using dlsym without .h file?
Also, how do you deal with the elements from the struct grabbed by dlsym? I know that you don't have the proper elements listed without .h file, and obviously some pointer shifting is necessary, but can anyone give me an example of how to do it?
Thanks
I would like to use some nss3.dll code in my program. To do this I decided to declare all of the compound datatypes that it needs and call the functions inside the dll file with them.
I am using a file in the firefox source code to see how to properly use the functions I need. In one of the functions it declares one of these compound datatypes (secuPWData) and passes it variables. Here is the definition I pasted into my code without any errors:
typedef struct {
enum {
PW_NONE = 0,
PW_FROMFILE = 1,
PW_PLAINTEXT = 2,
PW_EXTERNAL = 3
} source;
char *data;
} secuPWData;
The declaration of this struct looks like this in the code I'm looking at: secuPWData pwdata = { PW_NONE, NULL };
When I try to use a similar (or even the same) declaration, it complains about the PW_NONE attribute, claiming it is undefined. When I tried to pass in the 0 value in its place, it told me that 'a value of type "int" cannot be used to initialize an entity of type "enum secuPWData::"'. To try to debug the issue, I tried pasting the definition right on top of the declaration, without any change.
What is causing this problem to occur?
Thanks for any help.
just as #n.m. mentioned try using secuPWData::PW_NONE
#include <iostream>
using namespace std;
typedef struct {
enum {
PW_NONE = 0,
PW_FROMFILE = 1,
PW_PLAINTEXT = 2,
PW_EXTERNAL = 3
} source;
char *data;
} secuPWData;
int main() {
secuPWData pwdata = { secuPWData::PW_NONE, NULL };
return 0;
}
worked for me .. ideone - link
I saw someone writing code like this , in a C++ class:
int foo ( int dummy )
{
this->dummy = dummy;
}
Shall we use code like that , will it cause problems ?
I tried to compile something like this , it seems to be worked.
#update:
I posted this mostly about the name dummy , and the internal variable this->dummy , and if it's problem causing
That's perfectly fine for a member function, other than you're missing a return statement. dummy will shadow the member variable and so you use this-> to refer to member.
int foo ( int dummy )
{
this->dummy = dummy; // set member to argument
return this->dummy;
}
Don't do this for things more complex than a simple set function, as it's confusing.
int foo ( int dummy ) // Bad practise! Rename this param as the function isn't a setter
{
this->dummy = dummy * 2 + 1;
return this->dummy;
}
There is nothing wrong with doing that perse. It can get confusing though if you use dummy assuming it is coming from the class but its actually coming from the parameter.
IMO, its better to use something to denote it is a class member. Some people use simply mDummy, other m_Dummy, others just write dummy_.
Its up to you what you prefer but most of all you should be consistent.
The code is not fine. The function is defined as returning an int but there is no return statement. The compiler might only give a warning about this, but the function calling foo might expect it to return a valid value, which it doesn't, and bad stuff might happen.
You have to do it this way if you're passing a parameter with the same name as the member variable.
But it might be a better practice to avoid a hidden (member-)variable by using different names. There's different coding styles, some would use dummy_, some would use mDummy or other ways to name member variables. This makes your code less confusing.
Well there is nothing wrong with your use, but the code needs to return an int as its an int function :)
Dummy variable in your current class is assigned to the passed int, however do remember they are different but now pointing to the same thing, therefore its better to give it a different name as its in a different.
You could however loose precision under certain variable types.
#include <stddef.h>
typedef struct intlist {
int size;
int i[1];
} intlist;
intlist *
makeintlist (int size)
{
intlist *ilp = malloc (offsetof (intlist, i[size])); /* not C++ */
ilp->size = size;
return ilp;
}
member variable size is allocated to size
That will work.
Don't do it, it's confusing!
This c++ code is working fine , however memory validator says that I am using a deleted pointer in:
grf->filePath = fname; Do you have any idea why ? Thank you.
Dirloader.h
// Other code
class CDirLoader
{
public:
struct TKnownGRF
{
std::string filePath;
DWORD encodingType;
DWORD userDataLen;
char *userData;
};
// Other Code
CDirLoader();
virtual ~CDirLoader();
Dirloader.cpp
// Other code
void CDirLoader::AddGroupFile(const std::string& _fname)
{
// Other code including std::string fname = _fname;
TKnownGRF *grf = new TKnownGRF;
grf->filePath = fname;
delete grf; // Just for testing purposes
P.S.: This is only an code extract. Of course if I define a struct TKnownGRF inside .cpp and use it as an actual object, gfr.filepath = something, instead of pointer grf->filepath=something, than it is ok, but I do need to have it inside *.h in CDirLoader class, due to many other vector allocations.
Since the function returns void
void CDirLoader::AddGroupFile(const std::string& _fname)
the question is what are you going to do with grf?
Are you going to delete it? If so, then, why do a new? you can just declare a TKnownGRF variable on the stack! In that case, _fname is not contributing to the logic of this method.
I guess that the class CDirLoader has a member variable of type TKnownGRF, say grf_, and that need to be used in the AddsGroupFile() method, e.g.:
grf_.filepath = _fname;
Does this happen to be using an older version of STL, say, VC6, and running multithreaded? Older versions of STL's string class used a reference counted copy on write implementation, which didn't really work in a multithreaded environment. See this KB article on VC 6.
Or, it's also possible that you are looking at the wrong problem. If you call std::string::c_str() and cache the result at all, the cached result would probably be invalidated when you modified the original string. There are a few cases where you can get away with that, but it's very much implementation specific.
I'm a newbie at using the STL Algorithms and am currently stuck on a syntax error. My overall goal of this is to filter the source list like you would using Linq in c#. There may be other ways to do this in C++, but I need to understand how to use algorithms.
My user-defined function object to use as my function adapter is
struct is_Selected_Source : public std::binary_function<SOURCE_DATA *, SOURCE_TYPE, bool>
{
bool operator()(SOURCE_DATA * test, SOURCE_TYPE ref)const
{
if (ref == SOURCE_All)
return true;
return test->Value == ref;
}
};
And in my main program, I'm using as follows -
typedef std::list<SOURCE_DATA *> LIST;
LIST; *localList = new LIST;;
LIST* msg = GLOBAL_DATA->MessageList;
SOURCE_TYPE _filter_Msgs_Source = SOURCE_TYPE::SOURCE_All;
std::remove_copy(msg->begin(), msg->end(), localList->begin(),
std::bind1st(is_Selected_Source<SOURCE_DATA*, SOURCE_TYPE>(), _filter_Msgs_Source));
What I'm getting the following error in Rad Studio 2010. The error means "Your source file used a typedef symbol where a variable should appear in an expression. "
"E2108 Improper use of typedef 'is_Selected_Source'"
Edit -
After doing more experimentation in VS2010, which has better compiler diagnostics, I found the problem is that the definition of remove_copy only allows uniary functions. I change the function to uniary and got it to work.
(This is only relevant if you didn't accidentally omit some of your code from the question, and may not address the exact problem you're having)
You're using is_Selected_Source as a template even though you didn't define it as one. The last line in the 2nd code snippet should read std::bind1st(is_Selected_Source()...
Or perhaps you did want to use it as a template, in which case you need to add a template declaration to the struct.
template<typename SOURCE_DATA, typename SOURCE_TYPE>
struct is_Selected_Source : public std::binary_function<SOURCE_DATA *, SOURCE_TYPE, bool>
{
// ...
};
At a guess (though it's only a guess) the problem is that std::remove_copy expects a value, but you're supplying a predicate. To use a predicate, you want to use std::remove_copy_if (and then you'll want to heed #Cogwheel's answer).
I'd also note that:
LIST; *localList = new LIST;;
Looks wrong -- I'd guess you intended:
LIST *locallist = new LIST;
instead.