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  • How to use void*

    - by Rondogiannis Aristophanes
    I am imlementing a simple merge function and I have got stuck, as the compiler gives me errors that I cannot explain. Here is my merge function: void merge(void *a, int beg, int middle, int end, int (*cmp)(const void*, const void* { std::stack<void*> first; std::stack<void*> second; for(int i = beg; i < middle; i++) { first.push(a+i); } for(int i = middle; i < end; i++) { second.push(a+i); } for(int i = beg; i < end; i++) { if(first.empty()) { void *tmp = second.top(); second.pop(); a+i = tmp; } else if(second.empty()) { void *tmp = first.top(); first.pop(); a+i = tmp; } else if(cmp(first.top(), second.top())) { void *tmp = first.top(); first.pop(); a+i = tmp; } else { void *tmp = second.top(); second.pop(); a+i = tmp; } } } And here is the error: sort.h: In function `void merge(void*, int, int, int, int (*)(const void*, const void*))': sort.h:9: error: pointer of type `void *' used in arithmetic sort.h:12: error: pointer of type `void *' used in arithmetic sort.h:19: error: pointer of type `void *' used in arithmetic sort.h:19: error: non-lvalue in assignment sort.h:23: error: pointer of type `void *' used in arithmetic sort.h:23: error: non-lvalue in assignment sort.h:27: error: pointer of type `void *' used in arithmetic sort.h:27: error: non-lvalue in assignment sort.h:31: error: pointer of type `void *' used in arithmetic sort.h:31: error: non-lvalue in assignment Can anyone help me? TIA.

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  • Explain this C# code: byte* p = (byte*) (void*) Scan0;

    - by qulzam
    I found the code from the net in which i cant understand this line:- byte* p = (byte*)(void*)Scan0; There Scan0 is System.IntPtr. It is code of C#.Net. Plz Explain the above line. The complete code is given below. this is code to convert a image in grayscale. public static Image GrayScale(Bitmap b) { BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb); int stride = bmData.Stride; System.IntPtr Scan0 = bmData.Scan0; unsafe { byte* p = (byte*)(void*)Scan0; int nOffset = stride - b.Width * 3; byte red, green, blue; for (int y = 0; y < b.Height; ++y) { for (int x = 0; x < b.Width; ++x) { blue = p[0]; green = p[1]; red = p[2]; p[0] = p[1] = p[2] = (byte)(.299 * red + .587 * green + .114 * blue); p += 3; } p += nOffset; } } b.UnlockBits(bmData); return (Image)b; } I understand all the code but only have the problem on this line. byte* p = (byte*)(void*)Scan0;

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  • generic programming in C with void pointer.

    - by Nyan
    Hi everyone, even though it is possible to write generic code in C using void pointer(generic pointer), I find that it is quite difficult to debug the code since void pointer can take any pointer type without warning from compiler. (e.g function foo() take void pointer which is supposed to be pointer to struct, but compiler won't complain if char array is passed.) What kind of approach/strategy do you all use when using void pointer in C?

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  • How to pass a function in a function?

    - by SoulBeaver
    That's an odd title. I would greatly appreciate it if somebody could clarify what exactly I'm asking because I'm not so sure myself. I'm watching the Stanford videos on Programming Paradigms(that teacher is awesome) and I'm up to video five when he started doing this: void *lSearch( void* key, void* base, int elemSize, int n, int (*cmpFn)(void*, void*)) Naturally, I thought to myself, "Oi, I didn't know you could declare a function and define it later!". So I created my own C++ test version. int foo(int (*bar)(void*, void*)); int bar(void* a, void* b); int main(int argc, char** argv) { int *func = 0; foo(bar); cin.get(); return 0; } int foo(int (*bar)(void*, void*)) { int c(10), d(15); int *a = &c; int *b = &d; bar(a, b); return 0; } int bar(void* a, void* b) { cout << "Why hello there." << endl; return 0; } The question about the code is this: it fails if I declare function int *bar as a parameter of foo, but not int (*bar). Why!? Also, the video confuses me in the fact that his lSearch definition void* lSearch( /*params*/ , int (*cmpFn)(void*, void*)) is calling cmpFn in the definition, but when calling the lSearch function lSearch( /*params*/, intCmp ); also calls the defined function int intCmp(void* elem1, void* elem2); and I don't get how that works. Why, in lSearch, is the function called cmpFn, but defined as intCmp, which is of type int, not int* and still works? And why does the function in lSearch not have to have defined parameters?

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  • How can I free all allocated memory at once?

    - by Tommy
    Here is what I am working with: char* qdat[][NUMTBLCOLS]; char** tdat[]; char* ptr_web_data; // Loop thru each table row of the query result set for(row_index = 0; row_index < number_rows; row_index++) { // Loop thru each column of the query result set and extract the data for(col_index = 0; col_index < number_cols; col_index++) { ptr_web_data = (char*) malloc((strlen(Data) + 1) * sizeof(char)); memcpy (ptr_web_data, column_text, strlen(column_text) + 1); qdat[row_index][web_data_index] = ptr_web_data; } } tdat[row_index] = qdat[col_index]; After the data is used, the memory allocated is released one at a time using free(). for(row_index = 0; row_index < number_rows; row_index++) { // Loop thru all columns used for(col_index = 0; col_index < SARWEBTBLCOLS; col_index++) { // Free memory block pointed to by results set array free(tdat[row_index][col_index]); } } Is there a way to release all the allocated memory at once, for this array? Thank You.

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  • Get Function Pointer to function in a shared library I didn't directly load

    - by bdk
    My Linux application (A) links against a Third Party shared Library (B) which I don't have source code to. This library makes use of another third party shared library that I don't have source code to (C). I believe that (B) uses dlopen to access (C) instead of directly linking. My reasoning for this is that 'ldd' on (B) does not show (C) and objdump -X (B) shows references to dlopen/dlclose/dlsym. My requirement is that I need to in my code for (A) get a function pointer to a function foo() located in (C). Normally I'd use dlsym for this, but I need to pass it the handle returned from dlopen which I don't have since (B) does not expose this. - For the larger context: I need to modify the function in (C) such that everytime it calls its helper function bar() (also located in (C)), it also calls a function with the same signature located in (A) with the same parameters (Basically inject my code into the codepath of (C) foo()-bar(). I believe I've found a way to accomplish this using gdb, but in order to port my gdb command list, but I'm stuck on the step of getting the function pointer. I'm also open to alternatives to accomplish the same task rather than the exact problem as stated above Edit: After writing this I realized I can probably just do another dlopen on the file in my code and the symbols returned via dlsym on that handle should be the same as received via the original dlopen, If I'm reading the dlopen man page correctly. However I'm still interested in advice or assistance with the my larger context, If theres a better way to go about this

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  • From where starts the process' memory space and where does it end?

    - by nhaa123
    Hi, I'm trying to dump memory from my application where the variables lye. Here's the function: void MyDump(const void *m, unsigned int n) { const unsigned char *p = reinterpret_cast<const unsigned char *(m); char buffer[16]; unsigned int mod = 0; for (unsigned int i = 0; i < n; ++i, ++mod) { if (mod % 16 == 0) { mod = 0; std::cout << " | "; for (unsigned short j = 0; j < 16; ++j) { switch (buffer[j]) { case 0xa: case 0xb: case 0xd: case 0xe: case 0xf: std::cout << " "; break; default: std::cout << buffer[j]; } } std::cout << "\n0x" << std::setfill('0') << std::setw(8) << std::hex << (long)i << " | "; } buffer[i % 16] = p[i]; std::cout << std::setw(2) << std::hex << static_cast<unsigned int(p[i]) << " "; if (i % 4 == 0 && i != 1) std::cout << " "; } } Now, how can I know from which address starts my process memory space, where all the variables are stored? And how do I now, how long the area is? For instance: MyDump(0x0000 /* <-- Starts from here? */, 0x1000 /* <-- This much? */); Best regards, nhaa123

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  • operator "new" returning a non-local heap pointer for only one class ?

    - by KaluSingh Gabbar
    Language : C++ Platform : Windows Server 2003 I have an exe calling a DLL, in which when I allocate (new) the memory for class A (which is in DLL) it returns me a non-local heap pointer. I try to new other classes which are in DLL and "new" returns a valid heap pointer for them, its only Class A which is not being allocated properly. I am on windows and validating the heap by this function call : _CrtIsValidHeapPointer ( (const void *) pPtr ) I am seriously confused why this only happens with new-ing Class A and no other class ? (All Native Code)

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  • Getting value from pointer

    - by Eric
    Hi, I'm having problem getting the value from a pointer. I have the following code in C++: void* Nodo::readArray(VarHash& var, string varName, int posicion, float& d) { //some code before... void* res; float num = bit.getFloatFromArray(arregloTemp); //THIS FUNCTION RETURN A FLOAT AND IT'S OK cout << "NUMBER " << num << endl; d = num; res = &num; return res } int main() { float d = 0.0; void* res = n.readArray(v, "c", 0, d); //THE VALUES OF THE ARRAY ARE: {65.5, 66.5}; float* car3 = (float*)res; cout << "RESULT_READARRAY " << *car3 << endl; cout << "FLOAT REFERENCE: " << d << endl; } The result of running this code is the following: NUMBER 65.5 RESULT_READARRAY -1.2001 //INCORRECT IT SHOULD BE LIKE NUMBER FLOAT REFERENCE: 65.5 //CORRECT NUMBER 66.5 RESULT_READARRAY -1.2001 //INCORRECT IT SHOULD BE LIKE NUMBER FLOAT REFERENCE: 66.5 //CORRECT For some reason, when I get the value of the pointer returned by the function called readArray is incorrect. I'm passing a float variable(d) as a reference in the same function just to verify that the value is ok, and as you can see, THE FLOAT REFERENCE matches the NUMBER. If I declare the variable num(read array) as a static float, the first RESULT_READARRAY will be 65.5, that is correct, however, the next value will be the same instead of 66.5. Let me show you the result of running the code using static float variable: NUMBER 65.5 RESULT_READARRAY 65.5 //PERFECT FLOAT REFERENCE: 65.5 //¨PERFECT NUMBER 65.5 //THIS IS INCORRECT, IT SHOULD BE 66.5 RESULT_READARRAY 65.5 FLOAT REFERENCE: 65.5 Do you know how can I get the correct value returned by the function called readArray()?

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  • Remove pointer object whose reference is mantained in three different lists

    - by brainydexter
    I am not sure how to approach this problem: 'Player' class mantains a list of Bullet* objects: class Player { protected: std::list< Bullet* > m_pBullet_list; } When the player fires a Bullet, it is added to this list. Also, inside the constructor of bullet, a reference of the same object is updated in CollisionMgr, where CollisionMgr also mantains a list of Bullet*. Bullet::Bullet(GameGL*a_pGameGL, Player*a_pPlayer) : GameObject( a_pGameGL ) { m_pPlayer = a_pPlayer; m_pGameGL->GetCollisionMgr()->AddBullet(this); } class CollisionMgr { void AddBullet(Bullet* a_pBullet); protected: std::list< Bullet*> m_BulletPList; } In CollisionMgr.Update(); based on some conditions, I populate class Cell which again contain a list of Bullet*. Finally, certain conditions qualify a Bullet to be deleted. Now, these conditions are tested upon while iterating through a Cell's list. So, if I have to delete the Bullet object, from all these places, how should I do it so that there are no more dangling references to it? std::list< Bullet*>::iterator bullet_it; for( bullet_it = (a_pCell->m_BulletPList).begin(); bullet_it != (a_pCell->m_BulletPList).end(); bullet_it++) { bool l_Bullet_trash = false; Bullet* bullet1 = *bullet_it; // conditions would set this to true if ( l_Bullet_Trash ) // TrashBullet( bullet1 ); continue; } Also, I was reading about list::remove, and it mentions that it calls the destructor of the object we are trying to delete. Given this info, if I delete from one list, the object does not exist, but the list would still contain a reference to it..How do I handle all these problems ? Can someone please help me here ? Thanks PS: If you want me to post more code or provide explanation, please do let me know.

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  • Equivalent to window.setTimeout() for C++

    - by bobobobo
    In javascript there's this sweet, sweet function window.setTimeout( func, 1000 ) ; which will asynchronously invoke func after 1000 ms. I want to do something similar in C++ (without multithreading), so I put together a sample loop like: #include <stdio.h> struct Callback { // The _time_ this function will be executed. double execTime ; // The function to execute after execTime has passed void* func ; } ; // Sample function to execute void go() { puts( "GO" ) ; } // Global program-wide sense of time double time ; int main() { // start the timer time = 0 ; // Make a sample callback Callback c1 ; c1.execTime = 10000 ; c1.func = go ; while( 1 ) { // its time to execute it if( time c1.execTime ) { c1.func ; // !! doesn't work! } time++; } } How can I make something like this work?

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  • How can I pass a const array or a variable array to a function in C?

    - by CSharperWithJava
    I have a simple function Bar that uses a set of values from a data set that is passed in in the form of an Array of data structures. The data can come from two sources: a constant initialized array of default values, or a dynamically updated cache. The calling function determines which data is used and should be passed to Bar. Bar doesn't need to edit any of the data and in fact should never do so. How should I declare Bar's data parameter so that I can provide data from either set? union Foo { long _long; int _int; } static const Foo DEFAULTS[8] = {1,10,100,1000,10000,100000,1000000,10000000}; static Foo Cache[8] = {0}; void Bar(Foo* dataSet, int len);//example function prototype Note, this is C, NOT C++ if that makes a difference; Edit Oh, one more thing. When I use the example prototype I get a type qualifier mismatch warning, (because I'm passing a mutable reference to a const array?). What do I have to change for that?

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  • Incompatible types when assigning to type 'struct compartido'

    - by user1660559
    I have one problem with this code. I should create one structure and share it across 5 new process created from the father: #include <stdio.h> #include <stdlib.h> #include <sys/wait.h> #include <unistd.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> #include <sys/sem.h> #include <time.h> struct compartido { int pid1, pid2, pid3, pid4, pid5; int propietario; int contador; int pidpadre; }; struct compartido var; int main(int argc, char *argv[]) { key_t llave1,llavesem; int idmem,idsem; llave1=ftok("/tmp",'a'); idmem=shmget(llave1,sizeof(int),IPC_CREAT|0600); if (idmem==-1) { perror ("shmget"); return 1; } var=shmat(idmem,0,0); /*This line is giving the error*/ /*rest of the code*/ } The exact error is giving is: error: incompatible types when assigning to type 'struct compartido' from type 'void *' I need to put this structure in the shared variable to be able to see and modify all those data from the 6 process (5 children and the father). What I'm doing bad? Thanks in advance and best regards,

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  • Exposing boost::scoped_ptr in boost::python

    - by Rupert Jones
    Hello, I am getting a compile error, saying that the copy constructor of the scoped_ptr is private with the following code snippet: class a {}; struct s { boost::scoped_ptr<a> p; }; BOOST_PYTHON_MODULE( module ) { class_<s>( "s" ); } This example works with a shared_ptr though. It would be nice, if anyone knows the answer. Thanks

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  • Function Pointer

    - by Shaista Naaz
    How is that function pointer better than if-else or switch case? Is it because function pointer helps callback functions and thus promotes asynchronous implementation?

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  • Pass 2d array to function in C?

    - by Evelyn
    I know it's simple, but I can't seem to make this work. My function is like so: int GefMain(int array[][5]) { //do stuff return 1; } In my main: int GefMain(int array[][5]); int main(void) { int array[1800][5]; GefMain(array); return 0; } I referred to this helpful resource, but I am still getting the error "warning: passing argument 1 of GefMain from incompatible pointer type." What am I doing wrong?

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  • return an address of a double

    - by bks
    i'm having an issue understanding why the following works: void doubleAddr(double* source, double** dest) { *dest = source; } i get a pointer to a double and want to change the double that dest points to: //usage: int main() { double* num; double* dest; doubleAddr(num, &dest); return 0; } thanks in advance

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  • FORTRAN function returning an array causes a segfault (calling from C++)

    - by Dane Larsen
    Basically, here's my problem. I'm calling someone else's FORTRAN functions from my C++ code, and it's giving me headaches. Some code: function c_error_message() character(len = 255) :: c_error_message errmsg(1:9) = 'ERROR MSG' return end That's the FORTRAN function. My first question is: Is there anything in there that would cause a segfault? If not, then second: What does that return? A pointer? I'm trying to call it with the following C statement: char *e = c_error_message_(); That causes a segfault. c_error_message(); That too causes a segfault. I declared c_error_message_() earlier on with the following code: extern"C" { char* c_error_message_(); } Would declaring a function with a different return type than the actual return type cause a segfault? I'm at a loss. Thanks for any replies.

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  • [C] this code, its work fine and return what i want, but its hangs before print it ??

    - by Rami Jarrar
    I make this program :: #include<stdio.h> char *raw_input(char *msg); main() { char *s; *s = *raw_input("Message Here Is: "); printf("Return Done.."); printf(s); } char *raw_input(char *msg){ char *d; printf("%s", msg); scanf("%s",&d); return d; } What this do is, it print my message and scan for input from the user, then print it,, but whats the problem in print the input from the user ??? Update:: I need the raw_input func. call be like this without any extra *s = *raw_input("Message Here"); I dont want to use this :: raw_input("Message Here Is: ", d); .... Just want to return the string that the user will enter .

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