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  • How to assign a value to an pointer-pointer passed in call by reference?

    - by mystify
    I want to achieve something similar to what these guys do here: - (NSUInteger)countForFetchRequest:(NSFetchRequest *)request error:(NSError **)error like you can see, you pass an NSError pointer and that nice method will assign a real NSError object to your pointer in case there is an error. So the cool thing about this is, that the method returns an NSUInteger but can ALSO return an NSError, without having to mess around with ugly and fat arrays or dictionaries. So how could I assign an object to the passed-in error pointer?

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  • C++ vector of char array

    - by Stuart
    I am trying to write a program that has a vector of char arrays and am have some problems. char test [] = { 'a', 'b', 'c', 'd', 'e' }; vector<char[]> v; v.push_back(test); Sorry this has to be a char array because I need to be able to generate lists of chars as I am trying to get an output something like. a a a b a c a d a e b a b c Can anyone point me in the right direction? Thanks

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  • Assign bitset member to char

    - by RedX
    I have some code here that uses bitsets to store many 1 bit values into a char. Basically struct BITS_8 { char _1:1; (...) char _8:1; } Now i was trying to pass one of these bits as a parameter into a function void func(char bit){ if(bit){ // do something }else{ // do something else } // and the call was struct BITS_8 bits; // all bits were set to 0 before bits._7 = 1; bits._8 = 1; func(bits._8); The solution was to single the bit out when calling the function: func(bits._8 & 0x128); But i kept going into //do something because other bits were set. I was wondering if this is the correct behaviour or if my compiler is broken. The compiler is an embedded compiler that produces code for freescale ASICs.

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  • Initializing and accessing a pointer from an array of pointers

    - by idealistikz
    Suppose I have the following: void **Init(int numElems) { //What is the best way to intialize 'ptrElems' to store an array of void *'s? void **ptrElems = malloc(numElems * sizeof(void *)); return ptrElems; } //What is the best way to return a pointer pointing at the index passed as a parameter? void **GetPtr(void **ptrElems, int index) { void **elem = elems + (index * sizeof(void *)); return elem; } First, what is the best way to intialize 'ptrElems' to store an array of pointers? I use malloc because assigning it to an array will not persist after the end of the function. Second, what is the best way to point to the pointer at the specified index? I tried typecasting the first line of the 'GetPtr' function to ensure proper pointer arithmetic, but I receive the warning, 'initialization from incompatible pointer type'. Is it necessary to typecast?

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  • How do you delete a pointer without deleting the data the pointer points to?

    - by Faken
    I have a pointer that points to an array and another pointer referencing the same array. How do i delete any one of those pointers without killing the array such that the second undeleted pointer still works? for example: int* pointer1 = new int [1000]; int* pointer2; pointer2 = pointer1; Now i want to get rid of pointer1, how would i do it such that i can continue to access the array normaly through pointer2?

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  • Detect pointer arithmetics because of LARGEADDRESSAWARE

    - by Suma
    I would like to switch my application to LARGEADDRESSAWARE. One of issues to watch for is pointer arithmetic, as pointer difference can no longer be represented as signed 32b. Is there some way how to find automatically all instances of pointer subtraction in a large C++ project? If not, is there some "least effort" manual or semi-automatic method how to achieve this?

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  • Determining if Memory Pointer is Valid - C++

    - by Jim Fell
    It has been my observation that if free( ptr ) is called where ptr is not a valid pointer to system-allocated memory, an access violation occurs. Let's say that I call free like this: LPVOID ptr = (LPVOID)0x12345678; free( ptr ); This will most definitely cause an access violation. Is there a way to test that the memory location pointed to by ptr is valid system-allocated memory? It seems to me that the the memory management part of the Windows OS kernel must know what memory has been allocated and what memory remains for allocation. Otherwise, how could it know if enough memory remains to satisfy a given request? (rhetorical) That said, it seems reasonable to conclude that there must be a function (or set of functions) that would allow a user to determine if a pointer is valid system-allocated memory. Perhaps Microsoft has not made these functions public. If Microsoft has not provided such an API, I can only presume that it was for an intentional and specific reason. Would providing such a hook into the system prose a significant threat to system security? Situation Report Although knowing whether a memory pointer is valid could be useful in many scenarios, this is my particular situation: I am writing a driver for a new piece of hardware that is to replace an existing piece of hardware that connects to the PC via USB. My mandate is to write the new driver such that calls to the existing API for the current driver will continue to work in the PC applications in which it is used. Thus the only required changes to existing applications is to load the appropriate driver DLL(s) at startup. The problem here is that the existing driver uses a callback to send received serial messages to the application; a pointer to allocated memory containing the message is passed from the driver to the application via the callback. It is then the responsibility of the application to call another driver API to free the memory by passing back the same pointer from the application to the driver. In this scenario the second API has no way to determine if the application has actually passed back a pointer to valid memory.

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  • boost::function function pointer to parameters?

    - by high6
    How does boost::function take a function pointer and get parameters from it? I want wrap a function pointer so that it can be validated before being called. And it would be nice to be able to call it like boost::function is with the () operator and not having to access the function pointer member. Wrapper func; func(5); //Yes :D func.Ptr(5) //Easy to do, but not as nice looking

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  • char array split ip with strtok

    - by user1480139
    I'm trying to split a IP address like 127.0.0.1 from a file: using following C code: pch2 = strtok (ip,"."); printf("\npart 1 ip: %s",pch2); pch2 = strtok (NULL,"."); printf("\npart 2 ip: %s",pch2); And IP is a char ip[500], that containt an ip. When printing it prints 127 as part 1 but as part 2 it prints NULL? Can someone help me? EDIT: Whole function: FILE *file = fopen ("host.txt", "r"); char * pch; char * pch2; char ip[BUFFSIZE]; IPPart result; if (file != NULL) { char line [BUFFSIZE]; while(fgets(line,sizeof line,file) != NULL) { if(line[0] != '#') { //fputs(line,stdout); pch = strtok (line," "); printf ("%s\n",pch); strncpy(ip, pch, sizeof(pch)-1); ip[sizeof(pch)-1] = '\0'; //pch = strtok (line, " "); pch = strtok (NULL," "); printf("%s",pch); pch2 = strtok (ip,"."); printf("\nDeel 1 ip: %s",pch2); pch2 = strtok (NULL,"."); printf("\nDeel 2 ip: %s",pch2); //if(strcmp(pch,url) == 0) //{ // result.part1 = //} } } fclose(file); }

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  • Start a thread using a method pointer

    - by Michael
    Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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  • how to access char*** from dll import in C#

    - by mavrick
    I have a function in win32 dll with signature as: void func1(int a, char*** outData) int a -- input parameter char*** outData -- output parameter - pointer to array of char strings Any idea how to access this in C# using dll import & what should be the signature.

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  • [C++] Start a thread using a method pointer

    - by Michael
    Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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  • command&pointer&malloc [closed]

    - by gcc
    input 23 3 4 4 42 n 23 0 9 9 n n n 3 9 9 x //according to input,i should create int pointer arrays. pointer arrays starting from 1 (that is initial arrays is arrays[1].when program sees n ,it must be jumb to arrays 2 expected output arrays[1] 3 4 5 42 arrays[2] 23 0 9 9 arrays[5] 3 9 9 x is stopper n is comman to create new pointer array i am new in this site anyone help me how can i write

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  • Initialize void pointer to point to an array

    - by idealistikz
    Suppose I have the following: typedef struct { int itemSize; int count; void *list; } Mystruct; Mystruct *InitStruct(int itemSize, int count) { Mystruct *my = malloc(sizeof(Mystruct)); my->itemSize = itemSize; my->count = count; //What is the best way to initialize list? For example: //my->list = malloc(count * sizeof(void *)); OR //my->list = malloc(count * sizeof(itemSize)); } //The following should return a pointer to the element stored at a given index void *Retrieve(const MyStruct *my, int index) { void *item; //What is the best way to return a pointer to the item at the given index from //my->list? } Mystruct is similar to an array and void *list is supposed to store the elements or pointers to the elements. Mystruct *InitStruct is a function that initializes a Mystruct pointer and void *Retrieve is a function that returns a pointer to the element stored at a given index. First, how should I initialize void* list? Should it hold the actual elements or be an array of pointers pointing to the elements? Second, using the void *Retrieve function, how do I return a pointer to the element stored at a given index in my-list?

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  • c++: at what point should I start using "new char[N]" vs a static buffer "char[Nmax]"

    - by dan
    My question is with regard to C++ Suppose I write a function to return a list of items to the caller. Each item has 2 logical fields: 1) an int ID, and 2) some data whose size may vary, let's say from 4 bytes up to 16Kbytes. So my question is whether to use a data structure like: struct item { int field1; char field2[MAX_LEN]; OR, rather, to allocate field2 from the heap, and require the caller to destroy when he's done: struct item{ int field1; char *field2; // new char[N] -- destroy[] when done! Since the max size of field #2 is large, is makes sense that this would be allocated from the heap, right? So once I know the size N, I call field2 = new char[N], and populate it. Now, is this horribly inefficient? Is it worse in cases where N is always small, i.e. suppose I have 10000 items that have N=4?

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