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  • Numerical precision of double type in Visual C++ 2008 Express debugger

    - by damik
    I'm using Visual C++ 2008 Express Edition and when i debug code: double x = 0.2; I see in debugging tooltip on x 0.20000000000000001 but: typedef numeric_limits< double > double_limit; int a = double_limit::digits10 gives me: a = 15 Why results in debugger are longer than maybe ? What is this strange precision based on ? My CPU is Intel Core 2 Duo T7100

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  • C++0x: How can I access variadic tuple members by index at runtime?

    - by nonoitall
    I have written the following basic Tuple template: template <typename... T> class Tuple; template <uintptr_t N, typename... T> struct TupleIndexer; template <typename Head, typename... Tail> class Tuple<Head, Tail...> : public Tuple<Tail...> { private: Head element; public: template <uintptr_t N> typename TupleIndexer<N, Head, Tail...>::Type& Get() { return TupleIndexer<N, Head, Tail...>::Get(*this); } uintptr_t GetCount() const { return sizeof...(Tail) + 1; } private: friend struct TupleIndexer<0, Head, Tail...>; }; template <> class Tuple<> { public: uintptr_t GetCount() const { return 0; } }; template <typename Head, typename... Tail> struct TupleIndexer<0, Head, Tail...> { typedef Head& Type; static Type Get(Tuple<Head, Tail...>& tuple) { return tuple.element; } }; template <uintptr_t N, typename Head, typename... Tail> struct TupleIndexer<N, Head, Tail...> { typedef typename TupleIndexer<N - 1, Tail...>::Type Type; static Type Get(Tuple<Head, Tail...>& tuple) { return TupleIndexer<N - 1, Tail...>::Get(*(Tuple<Tail...>*) &tuple); } }; It works just fine, and I can access elements in array-like fashion by using tuple.Get<Index() - but I can only do that if I know the index at compile-time. However, I need to access elements in the tuple by index at runtime, and I won't know at compile-time which index needs to be accessed. Example: int chosenIndex = getUserInput(); cout << "The option you chose was: " << tuple.Get(chosenIndex) << endl; What's the best way to do this?

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  • Passing arguments to a C program

    - by Radhika
    Hi All, I was writing a C program where I use 6 variables a,b,c,d,e,f a,b,c are constant values which I should pass as an argument(command line) d,e,f are going to be size of arrays(which are a part of a structure) typedef struct { blah blah } ex; ex ex0[d]; I am very confused about how to pass all these as argument. Right now I have hard coded these values,which apparently I should not be doing.

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  • Using a map with set_intersection

    - by Robin Welch
    Not used set_intersection before, but I believe it will work with maps. I wrote the following example code but it doesn't give me what I'd expect: #include <map> #include <string> #include <iostream> #include <algorithm> using namespace std; struct Money { double amount; string currency; bool operator< ( const Money& rhs ) const { if ( amount != rhs.amount ) return ( amount < rhs.amount ); return ( currency < rhs.currency ); } }; int main( int argc, char* argv[] ) { Money mn[] = { { 2.32, "USD" }, { 2.76, "USD" }, { 4.30, "GBP" }, { 1.21, "GBP" }, { 1.37, "GBP" }, { 6.74, "GBP" }, { 2.55, "EUR" } }; typedef pair< int, Money > MoneyPair; typedef map< int, Money > MoneyMap; MoneyMap map1; map1.insert( MoneyPair( 1, mn[1] ) ); map1.insert( MoneyPair( 2, mn[2] ) ); map1.insert( MoneyPair( 3, mn[3] ) ); // (3) map1.insert( MoneyPair( 4, mn[4] ) ); // (4) MoneyMap map2; map1.insert( MoneyPair( 3, mn[3] ) ); // (3) map1.insert( MoneyPair( 4, mn[4] ) ); // (4) map1.insert( MoneyPair( 5, mn[5] ) ); map1.insert( MoneyPair( 6, mn[6] ) ); map1.insert( MoneyPair( 7, mn[7] ) ); MoneyMap out; MoneyMap::iterator out_itr( out.begin() ); set_intersection( map1.begin(), map1.end(), map2.begin(), map2.end(), inserter( out, out_itr ) ); cout << "intersection has " << out.size() << " elements." << endl; return 0; } Since the pair labelled (3) and (4) appear in both maps, I was expecting that I'd get 2 elements in the intersection, but no, I get: intersection has 0 elements. I'm sure this is something to do with the comparitor on the map / pair but can't figure it out.

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  • C++ forward declaration problem

    - by Thomas
    Hi, I have a header file that has some forward declarations but when I include the header file in the implementation file it gets included after the includes for the previous forward declarations and this results in an error like this. error: using typedef-name ‘std::ifstream’ after ‘class’ /usr/include/c++/4.2.1/iosfwd:145: error: ‘std::ifstream’ has a previous declaration. Whats the norm for working around this? Thanks in advance.

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  • C++: Unknown pointer size when forward declaring (error C2036)

    - by Rosarch
    In a header file, I have forward declared two members of a namespace: namespace Foo { struct Odp typedef std::vector<Odp> ODPVEC; }; class Bar { public: Foo::ODPVEC baz; // C2036 }; The error generated by the compiler is: error C2036: 'Foo::Odp *': unknown size I'm guessing this is an issue with forward declaring Odp. How can I get around this?

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  • Returning a struct pointer

    - by idealistikz
    Suppose I have the following struct and function returning a pointer: typedef struct { int num; void *nums; int size; } Mystruct; Mystruct *mystruct(int num, int size) { .... } I want to define any Mystruct pointer using the above function. Should I declare a Mystruct variable, define the properties of Mystruct, assign a pointer to it, and return the pointer or define the properties of a mystruct property through a pointer immediately?

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  • How can I prevent segmentation faults in my program?

    - by worlds-apart89
    I have a C assignment. It is a lot longer than the code shown below, and we are given the function prototypes and instructions only. I have done my best at writing code, but I am stuck with segmentation faults. When I compile and run the program below on Linux, at "735 NaN" it will terminate, indicating a segfault occurred. Why? What am I doing wrong? Basically, the program does not let me access table-list_array[735]-value and table-list_array[735]-key. This is of course the first segfault. There might be more following index 735. #include <stdio.h> #include <stdlib.h> typedef struct list_node list_node_t; struct list_node { char *key; int value; list_node_t *next; }; typedef struct count_table count_table_t; struct count_table { int size; list_node_t **list_array; }; count_table_t* table_allocate(int size) { count_table_t *ptr = malloc(sizeof(count_table_t)); ptr->size = size; list_node_t *nodes[size]; int k; for(k=0; k<size; k++){ nodes[k] = NULL; } ptr->list_array = nodes; return ptr; } void table_addvalue(count_table_t *table) { int i; for(i=0; i<table->size; i++) { table->list_array[i] = malloc(sizeof(list_node_t)); table->list_array[i]->value = i; table->list_array[i]->key = "NaN"; table->list_array[i]->next = NULL; } } int main() { count_table_t *table = table_allocate(1000); table_addvalue(table); int i; for(i=0; i<table->size; i++) printf("%d %s\n", table->list_array[i]->value, table->list_array[i]->key); return 0; }

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  • Why does this code sometimes return NaN?

    - by carrots
    This often returns NAN ("Not A Number") depending on input: #define PI 3.1415f GLfloat sineEaseIn(GLfloat ratio) { return 1.0f-cosf(ratio * (PI / 2.0f)); } I tried making PI a few digits smaller to see if that would help. No dice. Then I thought it might be a datatype mismatch, but float and glfloat seem to be equivalent: gl.h typedef float GLfloat; math.h extern float cosf( float ); Is this a casting issue?

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  • problem with fifos linux

    - by nunos
    I am having problem debugging why n_bytes in read_from_fifo function in client.c doesn't correspond to the value written to the fifo. It should only write 25 bytes but it tries to read a lot more (1836020505 bytes (!) to be exact). Any idea why this is happening? server.c: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> #include <sys/wait.h> #include <signal.h> #include <pthread.h> #include <sys/stat.h> typedef enum { false, true } bool; //first read the int with the number of bytes the data will have //then read that number of bytes bool read_from_fifo(int fd, char* var) { int n_bytes; if (read(fd, &n_bytes, sizeof(int))) { printf("going to read %d bytes\n", n_bytes); if (read(fd, var, n_bytes)) printf("read var\n"); else { printf("error in read var. errno: %d\n", errno); exit(-1); } } return true; } int main() { mkfifo("/tmp/foo", 0660); int fd = open("/tmp/foo", O_RDONLY); char var[100]; read_from_fifo(fd, var); printf("var: %s\n", var); return 0; } client.c: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> typedef enum { false, true } bool; //first write to fd a int with the number of bytes that will be written afterwards bool write_to_fifo(int fd, char* data) { int n_bytes = (strlen(data)) * sizeof(char); printf("going to write %d bytes\n", n_bytes); if (write(fd, &n_bytes, sizeof(int) != -1)) if (write(fd, data, n_bytes) != -1) return true; return false; } int main() { int fd = open("/tmp/foo", O_WRONLY); char data[] = "some random string abcdef"; write_to_fifo(fd, data); return 0; } Help is greatly appreciated. Thanks in advance.

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  • Calling cdecl Functions That Have Different Number of Arguments

    - by KlaxSmashing
    I have functions that I wish to call based on some input. Each function has different number of arguments. In other words, if (strcmp(str, "funcA") == 0) funcA(a, b, c); else if (strcmp(str, "funcB") == 0) funcB(d); else if (strcmp(str, "funcC") == 0) funcC(f, g); This is a bit bulky and hard to maintain. Ideally, these are variadic functions (e.g., printf-style) and can use varargs. But they are not. So exploiting the cdecl calling convention, I am stuffing the stack via a struct full of parameters. I'm wondering if there's a better way to do it. Note that this is strictly for in-house (e.g., simple tools, unit tests, etc.) and will not be used for any production code that might be subjected to malicious attacks. Example: #include <stdio.h> typedef struct __params { unsigned char* a; unsigned char* b; unsigned char* c; } params; int funcA(int a, int b) { printf("a = %d, b = %d\n", a, b); return a; } int funcB(int a, int b, const char* c) { printf("a = %d, b = %d, c = %s\n", a, b, c); return b; } int funcC(int* a) { printf("a = %d\n", *a); *a *= 2; return 0; } typedef int (*f)(params); int main(int argc, char**argv) { int val; int tmp; params myParams; f myFuncA = (f)funcA; f myFuncB = (f)funcB; f myFuncC = (f)funcC; myParams.a = (unsigned char*)100; myParams.b = (unsigned char*)200; val = myFuncA(myParams); printf("val = %d\n", val); myParams.c = (unsigned char*)"This is a test"; val = myFuncB(myParams); printf("val = %d\n", val); tmp = 300; myParams.a = (unsigned char*)&tmp; val = myFuncC(myParams); printf("a = %d, val = %d\n", tmp, val); return 0; } Output: gcc -o func func.c ./func a = 100, b = 200 val = 100 a = 100, b = 200, c = This is a test val = 200 a = 300 a = 600, val = 0

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  • How to store enum values in a NSMutableArray

    - by Oysio
    My problem is since an enum in objective-c essentially is an int value, I am not able to store it in a NSMutableArray. Apparently NSMutableArray won't take any c-date types like an int. Is there any common way to achieve this ? typedef enum { green, blue, red } MyColors; NSMutableArray *list = [[NSMutableArray alloc] initWithObjects: green, blue, red, nil]; //Get enum value back out MyColors greenColor = [list objectAtIndex:0];

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  • What's the C strategy to "imitate" a C++ template ?

    - by Andrei Ciobanu
    After reading some examples on stackoverflow, and following some of the answers for my previous questions (1), I've eventually come with a "strategy" for this. I've come to this: 1) Have a declare section in the .h file. Here I will define the data-structure, and the accesing interface. Eg.: /** * LIST DECLARATION. (DOUBLE LINKED LIST) */ #define NM_TEMPLATE_DECLARE_LIST(type) \ typedef struct nm_list_elem_##type##_s { \ type data; \ struct nm_list_elem_##type##_s *next; \ struct nm_list_elem_##type##_s *prev; \ } nm_list_elem_##type ; \ typedef struct nm_list_##type##_s { \ unsigned int size; \ nm_list_elem_##type *head; \ nm_list_elem_##type *tail; \ int (*cmp)(const type e1, const type e2); \ } nm_list_##type ; \ \ nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \ const type e2)); \ \ (...other functions ...) 2) Wrap the functions in the interface inside MACROS: /** * LIST INTERFACE */ #define nm_list(type) \ nm_list_##type #define nm_list_elem(type) \ nm_list_elem_##type #define nm_list_new(type,cmp) \ nm_list_new_##type##_(cmp) #define nm_list_delete(type, list, dst) \ nm_list_delete_##type##_(list, dst) #define nm_list_ins_next(type,list, elem, data) \ nm_list_ins_next_##type##_(list, elem, data) (...others...) 3) Implement the functions: /** * LIST FUNCTION DEFINITIONS */ #define NM_TEMPLATE_DEFINE_LIST(type) \ nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \ const type e2)) \ {\ nm_list_##type *list = NULL; \ list = nm_alloc(sizeof(*list)); \ list->size = 0; \ list->head = NULL; \ list->tail = NULL; \ list->cmp = cmp; \ }\ void nm_list_delete_##type##_(nm_list_##type *list, \ void (*destructor)(nm_list_elem_##type elem)) \ { \ type data; \ while(nm_list_size(list)){ \ data = nm_list_rem_##type(list, tail); \ if(destructor){ \ destructor(data); \ } \ } \ nm_free(list); \ } \ (...others...) In order to use those constructs, I have to create two files (let's call them templates.c and templates.h) . In templates.h I will have to NM_TEMPLATE_DECLARE_LIST(int), NM_TEMPLATE_DECLARE_LIST(double) , while in templates.c I will need to NM_TEMPLATE_DEFINE_LIST(int) , NM_TEMPLATE_DEFINE_LIST(double) , in order to have the code behind a list of ints, doubles and so on, generated. By following this strategy I will have to keep all my "template" declarations in two files, and in the same time, I will need to include templates.h whenever I need the data structures. It's a very "centralized" solution. Do you know other strategy in order to "imitate" (at some point) templates in C++ ? Do you know a way to improve this strategy, in order to keep things in more decentralized manner, so that I won't need the two files: templates.c and templates.h ?

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  • compiling OpenCV on Mac OS X Snow Leopard gets error: ‘Movie’ does not name a type

    - by moldov
    When I'm trying to compile OpenCV on Mac OS X Snow Leopard I recieve an error highgui/cvcap_qt.cpp:76: error: ‘Movie’ does not name a type There is a structure /// Movie state structure for QuickTime movies typedef struct CvCapture_QT_Movie { Movie myMovie; // movie handle GWorldPtr myGWorld; // we render into an offscreen GWorld But I don't know this type is described. I think in Quicktime but Quicktime is included // Mac OS includes include include include So I cannot build it.

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  • Writing a managed wrapper for unmanaged (C++) code - custom types/structs

    - by Bobby
    faacEncConfigurationPtr FAACAPI faacEncGetCurrentConfiguration( faacEncHandle hEncoder); I'm trying to come up with a simple wrapper for this C++ library; I've never done more than very simple p/invoke interop before - like one function call with primitive arguments. So, given the above C++ function, for example, what should I do to deal with the return type, and parameter? FAACAPI is defined as: #define FAACAPI __stdcall faacEncConfigurationPtr is defined: typedef struct faacEncConfiguration { int version; char *name; char *copyright; unsigned int mpegVersion; unsigned long bitRate; unsigned int inputFormat; int shortctl; psymodellist_t *psymodellist; int channel_map[64]; } faacEncConfiguration, *faacEncConfigurationPtr; AFAIK this means that the return type of the function is a reference to this struct? And faacEncHandle is: typedef struct { unsigned int numChannels; unsigned long sampleRate; ... SR_INFO *srInfo; double *sampleBuff[MAX_CHANNELS]; ... double *freqBuff[MAX_CHANNELS]; double *overlapBuff[MAX_CHANNELS]; double *msSpectrum[MAX_CHANNELS]; CoderInfo coderInfo[MAX_CHANNELS]; ChannelInfo channelInfo[MAX_CHANNELS]; PsyInfo psyInfo[MAX_CHANNELS]; GlobalPsyInfo gpsyInfo; faacEncConfiguration config; psymodel_t *psymodel; /* quantizer specific config */ AACQuantCfg aacquantCfg; /* FFT Tables */ FFT_Tables fft_tables; int bitDiff; } faacEncStruct, *faacEncHandle; So within that struct we see a lot of other types... hmm. Essentially, I'm trying to figure out how to deal with these types in my managed wrapper? Do I need to create versions of these types/structs, in C#? Something like this: [StructLayout(LayoutKind.Sequential)] struct faacEncConfiguration { uint useTns; ulong bitRate; ... } If so then can the runtime automatically "map" these objects onto eachother? And, would I have to create these "mapped" types for all the types in these return types/parameter type hierarchies, all the way down until I get to all primitives? I know this is a broad topic, any advice on getting up-to-speed quickly on what I need to learn to make this happen would be very much appreciated! Thanks!

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  • How can I declare a pointer structure?

    - by Y_Y
    This probably is one of the easiest questions ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head?

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  • decltype, result_of, or typeof?

    - by Neil G
    I have: class A { public: B toCPD() const; And: template<typename T> class Ev { public: typedef result_of(T::toCPD()) D; After instantiating Ev<A>, the compiler says: meta.h:12: error: 'T::toCPD' is not a type neither decltype nor typeof work either.

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  • g++ linker error--typeinfo, but not vtable

    - by James
    I know the standard answer for a linker error about missing typeinfo usually also involves vtable and some virtual function that I forgot to actually define. I'm fairly certain that's not the situation this time. Here's the error: UI.o: In function boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::Resource::GroupByState>(boost::shared_ptr<Graphics::Resource::GroupByState> const&, boost::detail::dynamic_cast_tag)': UI.cpp:(.text._ZN5boost10shared_ptrIN8Graphics7Widgets9WidgetSetEEC1INS1_8Resource12GroupByStateEEERKNS0_IT_EENS_6detail16dynamic_cast_tagE[boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::Resource::GroupByState>(boost::shared_ptr<Graphics::Resource::GroupByState> const&, boost::detail::dynamic_cast_tag)]+0x30): undefined reference totypeinfo for Graphics::Widgets::WidgetSet' Running c++filt on the obnoxious mangled name shows that it actually is looking at .boost::shared_ptr::shared_ptr(boost::shared_ptr const&, boost::detail::dynamic_cast_tag) The inheritance hierarchy looks something like class AbstractGroup { typedef boost::shared_ptr<AbstractGroup> Ptr; ... }; class WidgetSet : public AbstractGroup { typedef boost::shared_ptr<WidgetSet> Ptr; ... }; class GroupByState : public AbstractGroup { ... }; Then there's this: class UI : public GroupByState { ... void LoadWidgets( GroupByState::Ptr resource ); }; Then the original implementation: void UI::LoadWidgets( GroupByState::Ptr resource ) { WidgetSet::Ptr tmp( boost::dynamic_pointer_cast< WidgetSet >(resource) ); if( tmp ) { ... } } Stupid error on my part (trying to cast to a sibling class with a shared parent), even if the error is kind of cryptic. Changing to this: void UI::LoadWidgets( AbstractGroup::Ptr resource ) { WidgetSet::Ptr tmp( boost::dynamic_pointer_cast< WidgetSet >(resource) ); if( tmp ) { ... } } (which I'm fairly sure is what I actually meant to be doing) left me with a very similar error: UI.o: In function boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::_Drawer::Group>(boost::shared_ptr<Graphics::_Drawer::Group> const&, boost::detail::dynamic_cast_tag)': UI.cpp:(.text._ZN5boost10shared_ptrIN8Graphics7Widgets9WidgetSetEEC1INS1_7_Drawer5GroupEEERKNS0_IT_EENS_6detail16dynamic_cast_tagE[boost::shared_ptr<Graphics::Widgets::WidgetSet>::shared_ptr<Graphics::_Drawer::Group>(boost::shared_ptr<Graphics::_Drawer::Group> const&, boost::detail::dynamic_cast_tag)]+0x30): undefined reference totypeinfo for Graphics::Widgets::WidgetSet' collect2: ld returned 1 exit status dynamic_cast_tag is just an empty struct in boost/shared_ptr.hpp. It's just a guess that boost might have anything at all to do with the error. Passing in a WidgetSet::Ptr totally eliminates the need for a cast, and it builds fine (which is why I think there's more going on than the standard answer for this question). Obviously, I'm trimming away a lot of details that might be important. My next step is to cut it down to the smallest example that fails to build, but I figured I'd try the lazy way out and take a stab on here first. TIA!

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  • A simple question about type coercion in C++

    - by David
    Given a function prototype, and a type definition: int my_function(unsigned short x); typedef unsigned short blatherskite; Is the following situation defined by standard: int main(int argc, char** argv) { int result; blatherskite b; b=3; result = my_function(b); } Do I get type coercion predictably via the function prototype?

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  • How to initialize const float32x4x4_t (ARM NEON intrinsic, GCC) ?

    - by Eonil
    I can initialize float32x4_t like this: const float32x4x4_t = { 0.0f, 0.0f, 0.0f, 0.0f }; But this code makes an error Incompatible types in initializer: const float32x4x4_t = { 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, }; float32x4x4_t is 4x4 matrix built as: typedef struct float32x4x4_t { float32x4_t val[4]; } float32x4x4_t; How can I initialize this const struct?

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  • complex arguments for function

    - by myPost1
    My task is to create function funCall taking four arguments : pointer for 2d array of ints that stores pairs of numbers variable int maintaining number of numbers in 2d array pointer for table of pointers to functions int variable storing info about number of pointers to functions I was thinking about something like this : typedef int(*funPtr)(int, int); funPtr arrayOfFuncPtrs[]; void funCall( *int[][]k, int a, *funPtr z, int b); { }

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