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  • allocator with no template

    - by Merni
    Every stl container take an allocator as a second object, template < class T, class Allocator = allocator<T> > class vector; If you write your own class It is possible to use your own allocator. But is it possible to write your own allocator without using templates? For example, writing this function is not easy if you are not allowed to use templates pointer allocate(size_type n, const_pointer = 0) { void* p = std::malloc(n * sizeof(T)); if (!p) throw std::bad_alloc(); return static_cast<pointer>(p); } Because how could you know the size of T?

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  • Method sscanf() ambiguous behavior

    - by Carmen Cojocaru
    I am trying to understand how sscanf() works. I ran some examples from this page: http://docs.roxen.com/pike/7.0/tutorial/strings/sscanf.xml and they don't work on my platform. I can't understand why. For instance: "sscanf("4711bar", "%d%s", a, b);" makes the program exit with an error... Here is one of the examples that work: "sscanf("foo", "f%s", a);". Does anybody know why? Do they work on your platforms? Thank you. This is my code: int main(void){ char *b = (char*)malloc(sizeof(char)*100); int a = 0; sscanf("4711bar", "%d%s", a, b); printf("%d", a); printf("%s", b); }

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  • Allocating memory in char * struct

    - by mrblippy
    hi, im trying to read in a word from a user, then dynamically allocate memory for the word and store it in a struct array that contains a char *. i keep getting a implicit declaration of function âstrlenâ so i know im going wrong somewhere. struct class { char class_code[7]; char *name; }; char buffer[101]; struct unit units[1000]; scanf("%s", buffer); units[0].name = (char *) malloc(strlen(buffer)+1); strcpy(units[0].name, buffer);

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  • Allocating memory for a char pointer that is part of a struct

    - by mrblippy
    hi, im trying to read in a word from a user, then dynamically allocate memory for the word and store it in a struct array that contains a char *. i keep getting a implicit declaration of function âstrlenâ so i know im going wrong somewhere. struct class { char class_code[4]; char *name; }; char buffer[101]; struct unit units[1000]; scanf("%s", buffer); units[0].name = (char *) malloc(strlen(buffer)+1); strcpy(units[0].name, buffer);

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  • MACRO Question: Returning pointer to a certain value

    - by Andrei Ciobanu
    Is it possible to write a MACRO that has a type and a value as its input parameters (MACRO(type,value)), and returns a valid pointer to a location that holds the submitted value. This macro should perform like the following function, but in a more generic manner: int *val_to_ptr(int val){ int *r = NULL; r = nm_malloc(sizeof(*r)); *r = val; return r; } Where nm_malloc() is a failsafe malloc. The Macro usage should be compatible with this usage: printf("%d",*MACRO(int,5)); Is it possible to achieve that ?

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  • C - memset segfault for statically allocated char array

    - by user1327031
    I get a segfault when trying to memset an array of chars that was allocated statically, but not for an array of the same length that was allocated using malloc. variable definitions: //static char inBuff[IN_BUFF_LEN]; //dynamic char * inBuffD; function call: //static, cast used because char** != char (*) [n] serverInit(portNum, (char**) &inBuff, &serv_addr, &sockfd) //dynamic serverInit(portNum, &inBuffD, &serv_addr, &sockfd) use within the function: memset(*inBuffAdr, 0, IN_BUFF_LEN); I suspect that my problem is in the difference of the function calls, or to be more precise, my incomplete understanding of the "char** != char (*) [n]" situation. But I have been banging at this for too long and can't see the forest from the trees so any hints and advice would be very appreciated.

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  • user buffer after doing 'write' to file opened with O_DIRECT

    - by user1868481
    I'm using the O_DIRECT flag to write to the disk directly from the user buffer. But as far as I understand, Linux doesn't guarantee that after this call, the data is written. It just writes directly from the user buffer to the physical device using DMA or anything else... Therefore, I don't understand if I can write to the user buffer after the call to 'write' function. I'm sure that example code will help to understand my question: char *user_buff = malloc(...); /* assume it is aligned as needed */ fd = open(..., O_DIRECT); write(fd, ...) memset(user_buff, 0, ...) Is the last line (memset) legal? Is writing to the user buffer valid that is maybe used by DMA to transfer data to the device?

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  • How to compare two char* variables

    - by davit-datuashvili
    Suppose we have the following method (it is in c code): const char *bitap_search(const char *text, const char *pattern) My question is how can I compare text and pattern if they are char? This method is like a substring problem but I am confused a bit can I write in term of char such code? if (text[i]==pattern[i])? look i am interesting at this algorithm in java http://en.wikipedia.org/wiki/Bitap_algorithm how implement this in java? R = malloc((k+1) * sizeof *R); and please help me to translate this code in java

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  • Has anyone properly interpreted HTTP request based on this demo of winpcap?

    - by httpinterpret
    The example is here, and I tried it by changing the filter to tcp and dst port 80 and the following: void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data) { .... ip_len = (ih->ver_ihl & 0xf) * 4; tcp_len = (((u_char*)ih)[ip_len + 12] >> 4) * 4; tcpPayload = (u_char*)ih + ip_len + tcp_len; /* start of url - skip "GET " */ url = tcpPayload + 4; end_url = strchr((char*)url, ' '); url_length = end_url - url; final_url = (u_char*)malloc(url_length + 1); strncpy((char*)final_url, (char*)url, url_length); final_url[url_length] = '\0'; printf("%s\n", final_url); .... } But through debug, I see tcpPayload is full of messy code,not supposed "GET ..." stuff. What's wrong with my implement?

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  • Using sizeof with a dynamically allocated array

    - by robUK
    Hello, gcc 4.4.1 c89 I have the following code snippet: #include <stdlib.h> #include <stdio.h> char *buffer = malloc(10240); /* Check for memory error */ if(!buffer) { fprintf(stderr, "Memory error\n"); return 1; } printf("sizeof(buffer) [ %d ]\n", sizeof(buffer)); However, the sizeof(buffer) always prints 4. I know that a char* is only 4 bytes. However, I have allocated the memory for 10kb. So shouldn't the size be 10240? I am wondering am I thinking right here? Many thanks for any suggestions,

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  • C++ vector and struct problem win32

    - by ~james2432
    I have a structure defined in my header file: struct video { wchar_t* videoName; std::vector<wchar_t*> audio; std::vector<wchar_t*> subs; }; struct ret { std::vector<video*> videos; wchar_t* errMessage; }; struct params{ HWND form; wchar_t* cwd; wchar_t* disk; ret* returnData; }; When I try to add my video structure to a vector of video* I get access violation reading 0xcdcdcdc1 (videoName is @ 0xcdcdcdcd, before I allocate it) //extract of code where problem is video v; v.videoName = (wchar_t*)malloc((wcslen(line)+1)*sizeof(wchar_t)); wcscpy(v.videoName,line); p->returnData->videos.push_back(&v); //error here

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  • Operators vs Functions in C/C++

    - by user356106
    Someone recently asked me the difference between a C++ standard operator (e.g. new,delete,sizeof) and function (e.g. tan,delete, malloc). By "standard" I mean those provided by default by the compiler suite, and not user defined. Below were the answers I gave, though neither seemed satisfactory. (1) An operator doesn't need any headers to be included to use it : E.g. you can have a call to new without including any headers. However, a function (say free() ) does need headers included, compulsorily. (2) An operator is defined as such (ie as a class operator) somewhere in the standard headers. A function isn't. Can you critique these answers and give me a better idea of the difference?

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  • C++: How to make comparison function for char arrays?

    - by Newbie
    Is this possible? i get weird error message when i put char as the type: inline bool operator==(const char *str1, const char *str2){ // ... } Error message: error C2803: 'operator ==' must have at least one formal parameter of class type ... which i dont understand at all. I was thinking if i could directly compare stuff like: const char *str1 = "something"; const char *str2 = "something else"; const char str3[] = "lol"; // not sure if this is same as above and then compare: if(str1 == str2){ // ... } etc. But i also want it to work with: char *str = new char[100]; and: char *str = (char *)malloc(100); I am assuming every char array i use this way would end in NULL character, so the checking should be possible, but i understand it can be unsafe etc. I just want to know if this is possible to do, and how.

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  • seg violation using pycapsule_new

    - by user1733051
    I am trying some simple c API, where I am using PyCapsule_New to encapsulate a pointer. I am running into segment violation, can some body help me. mystruct *func1(int streamno, char mode,unsigned int options) { char * s; s=malloc(100); return s; } PyObject *Wrapper_func1(PyObject *self, PyObject *args) { int streamno; char mode; unsigned int options; mystruct* result; if (!PyArg_ParseTuple(args,"icI",&streamno,&mode,&options)) return NULL; result = func1(streamno,mode,options); return PyCapsule_New( result,NULL,NULL); }

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  • finding character in string C language

    - by iSight
    Hi, I am searching a character at first occurence in string using the following code. But, it is taking some time when the character is too long or the character that i am searching is at far extend, which makes delay in other operations. How could i tackle with this problem. The code is below here. Note: attrPtr is a char* which holds a reference to a string containing '"' character at far extend. int position = 0; char qolon = '"';//character to search while (*(attrPtr + position++) != qolon); char* attrValue = NULL; attrValue = (char*)malloc(position * sizeof(char)); strncpy(attrValue, attrPtr, position-1);

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  • Which to use - "operator new" or "operator new[]" - to allocate a block of raw memory in C++?

    - by sharptooth
    My C++ program needs a block of uninitialized memory. In C I would use malloc() and later free(). In C++ I can either call ::operator new or ::operator new[] and ::operator delete or operator delete[] respectively later. Looks like both ::operator new and ::operator new[] have exactly the same signature and exactly the same behavior. The same for ::operator delete and ::operator delete[]. The only thing I shouldn't do is pairing operator new with operator delete[] and vice versa - undefined behavior. Other than that which pair do I choose and why?

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  • Stucture with array of pointers in C

    - by MVTCplusplus
    What's wrong with this? Can I have an array of pointers to SDL_Surfaces in a struct in C? typedef struct { int next_wheel; int pos_X; int pos_Y; int front_wheel_pos_X; int front_wheel_pos_Y; int velocity; int rear_wheel_pos_X; int rear_wheel_pos_Y; SDL_Surface* body; SDL_Surface* rear_wheel[9]; SDL_Surface* front_wheel[9]; } mars_rover; ... mars_rover* init_rover() { mars_rover* rover = (mars_rover*)malloc(sizeof(mars_rover) + sizeof(SDL_Surface) * 19); ... return rover; } int main() { mars_rover* rover = init_rover(); ... }

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  • Why did this code still work?

    - by bstullkid
    Some old code that I just came across: MLIST * new_mlist_link() { MLIST *new_link = (MLIST * ) malloc(sizeof(MLIST)); new_link->next = NULL; new_link->mapi = NULL; new_link->result = 0; } This was being called to build a linked list, however I noticed there is no statement: return new_link; Even without the return statement there, the list still got built properly. Why did this happen? EDT: Platform: Mandriva 2009 64bit Linux 2.6.24.7-server GCC 4.2.3-6mnb1

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  • Same memory space being allocated again & again

    - by shadyabhi
    In each loop iteration, variable j is declared again and again. Then why is its address remaining same? Shouldn't it be given some random address each time? Is this compiler dependent? #include<stdio.h> #include<malloc.h> int main() { int i=3; while (i--) { int j; printf("%p\n", &j); } return 0; } Testrun:- shadyabhi@shadyabhi-desktop:~/c$ gcc test.c shadyabhi@shadyabhi-desktop:~/c$ ./a.out 0x7fffc0b8e138 0x7fffc0b8e138 0x7fffc0b8e138 shadyabhi@shadyabhi-desktop:~/c$

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  • assignment from incompatible pointer type

    - by Hristo
    I have set up the following struct: typedef struct _thread_node_t { pthread_t thread; struct thread_node_t *next; } thread_node_t; ... and then I have defined: // create thread to for incoming connection thread_node_t *thread_node = (thread_node_t*) malloc(sizeof(thread_node_t)); pthread_create(&(thread_node->thread), NULL, client_thread, &csFD); thread_node->next = thread_arr; // assignment from incompatible pointer type thread_arr = thread_node; where thread_arr is thread_node_t *thread_arr = NULL; I don't understand why the compiler is complaining. Maybe I'm misunderstanding something.

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  • How to fill a structure when a pointer to it, is passed as an argument to a function

    - by Ram
    I have a function: func (struct passwd* pw) { struct passwd* temp; struct passwd* save; temp = getpwnam("someuser"); /* since getpwnam returns a pointer to a static * data buffer, I am copying the returned struct * to a local struct. */ if(temp) { save = malloc(sizeof *save); if (save) { memcpy(save, temp, sizeof(struct passwd)); /* Here, I have to update passed pw* with this save struct. */ *pw = *save; /* (~ memcpy) */ } } } The function which calls func(pw) is able to get the updated information. But is it fine to use it as above. The statement *pw = *save is not a deep copy. I do not want to copy each and every member of structure one by one like pw-pw_shell = strdup(save-pw_shell) etc. Is there any better way to do it? Thanks.

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  • strategy to allocate/free lots of small objects

    - by aaa
    hello I am toying with certain caching algorithm, which is challenging somewhat. Basically, it needs to allocate lots of small objects (double arrays, < 256 elements), with objects accessible through mapped value, map[key] = array. time to initialized array may be quite large, generally more than 10 thousand cpu cycles. By lots I mean around gigabyte in total. objects may need to be popped/pushed as needed, generally in random places, one object at a time. lifetime of an object is generally long, minutes or more, however, object may be subject to allocation/deallocation several times during duration of program. What would be good strategy to avoid memory fragmentation, while still maintaining reasonable allocate deallocate speed? I am using C++, so I can use new and malloc. Thanks. I know there a similar questions on website, http://stackoverflow.com/questions/2156745/efficiently-allocating-many-short-lived-small-objects, are somewhat different, thread safety is not immediate issue for me.

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  • casting char* to char**

    - by blue_whale
    I am having a tough time understanding the following piece of code: int stride = 512; int max_len = 1024 * stride; char *addr = (char *)malloc(max_len); for (int i=stride; i<max_len; i += stride) *(char **)&addr[i-stride] = (char*)&addr[i]; *(char **)&addr[i-stride] = (char*)&addr[0]; Looking at the code it seems this is trying to create some kind of circular link list. But I have no clue what those casts are actually doing.

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  • How to get the Drive letter and Mount Path - MSDN

    - by new
    Hello all, I get the devices list from the system using SetupDiGetClassDevs Function - MSDN. Also i can able to get the vendor id and product id from the devices. But i cant able to get the drive letter and the mount path For Example if i plug the usb drive means , i have to get the drive letter like "G:/" Please help me to get the drive letter and mount path for the devices if (SetupDiEnumDeviceInterfaces(hDevInfo, NULL,&GUID_DEVINTERFACE_USB_DEVICE,i,&Interface_Info)) { wprintf(L"\tDeviccvcvcveInstanceId : %d\n", i); pspdidd->cbSize = sizeof(*pspdidd); SP_DEVICE_INTERFACE_DETAIL_DATA *pDetData = NULL; DWORD dwDetDataSize = sizeof (SP_DEVICE_INTERFACE_DETAIL_DATA) + 256; pDetData = (SP_DEVICE_INTERFACE_DETAIL_DATA*) malloc (dwDetDataSize); pDetData->cbSize = sizeof (SP_DEVICE_INTERFACE_DETAIL_DATA); SetupDiGetDeviceInterfaceDetail(hDevInfo,&Interface_Info,pDetData,dwDetDataSize, NULL,&DeviceInfoData); qDebug ()<<QString::fromWCharArray( pDetData->DevicePath ); }

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  • How to find out the format of a float?

    - by cannyboy
    I'm working with someone else's code, and there is a float with some unusual qualities. If I output the float using: NSLog(@"theFloat: %f", record.theFloat); I get: theFloat: 0.000000 However, if I use: NSLog(@"(int)theFloat = %i", (int) record.theFloat); I get: (int)theFloat: 71411232 How do I discover the real format and value of theFloat? I know that it should contain a large number. Incidentally, the Record class which contains the float propertizes it in such a way: @property (assign) float* theFloat; There is also floatLength: @property (assign) int floatLength; And has this method, which seems to indicate that the float is of variable length (?): - (void) copyFloat:(float*)theF ofLength:(int)len { float *floatcopy = malloc(len*sizeof(float)); memcpy(floatcopy, theF, len*sizeof(float)); self.theFloat = floatcopy; }

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