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  • How do you dynamically allocate a contiguous 3D array in C?

    - by Derek
    In C, I want to loop through an array in this order for(int z = 0; z < NZ; z++) for(int x = 0; x < NX; x++) for(int y = 0; y < NY; y++) 3Darray[x][y][z] = 100; How do I create this array in such a way that 3Darray[0][1][0] comes right before 3Darray[0][2][0] in memory? I can get an initialization to work that gives me "z-major" ordering, but I really want a y-major ordering for this 3d array This is the code I have been trying to use: char *space; char ***Arr3D; int y, z; ptrdiff_t diff; space = malloc(X_DIM * Y_DIM * Z_DIM * sizeof(char)) Arr3D = malloc(Z_DIM * sizeof(char **)); for (z = 0; z < Z_DIM; z++) { Arr3D[z] = malloc(Y_DIM * sizeof(char *)); for (y = 0; y < Y_DIM; y++) { Arr3D[z][y] = space + (z*(X_DIM * Y_DIM) + y*X_DIM); } }

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  • C - Malloc or calloc...and how?

    - by Pedro
    Hi...i have a txt file where the first number define the size of the array's, i know that calloc or malloc can reserve memory, but how? this code: typedef struct alpha{ int *size; char name; int tot; char line[60]; }ALPHA; fgets(line,60,fp); tot=atoi(line); size=(int*)calloc(name,sizeof(int); Imagine that in the first line of the txt is the number 10, wiht this code the size of name will be 10? like name[10]???

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  • Dynamic memory inside a struct

    - by Maximilien
    Hello, I'm editing a piece of code, that is part of a big project, that uses "const's" to initialize a bunch of arrays. Because I want to parametrize these const's I have to adapt the code to use "malloc" in order to allocate the memory. Unfortunately there is a problem with structs: I'm not able to allocate dynamic memory in the struct itself. Doing it outside would cause to much modification of the original code. Here's a small example: int globalx,globaly; struct bigStruct{ struct subStruct{ double info1; double info2; bool valid; }; double data; //subStruct bar[globalx][globaly]; subStruct ** bar=(subStruct**)malloc(globalx*sizeof(subStruct*)); for(int i=0;i<globalx;i++) bar[i]=(*subStruct)malloc(globaly*sizeof(subStruct)); }; int main(){ globalx=2; globaly=3; bigStruct foo; for(int i=0;i<globalx;i++) for(int j=0;j<globaly;j++){ foo.bar[i][j].info1=i+j; foo.bar[i][j].info2=i*j; foo.bar[i][j].valid=(i==j); } return 0; } Note: in the program code I'm editing globalx and globaly were const's in a specified namespace. Now I removed the "const" so they can act as parameters that are set exactly once. Summarized: How can I properly allocate memory for the substruct inside the struct? Thank you very much! Max

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  • Simple dynamic memory allocation bug.

    - by M4design
    I'm sure you (pros) can identify the bug's' in my code, I also would appreciate any other comments on my code. BTW, the code crashes after I run it. #include <stdlib.h> #include <stdio.h> #include <stdbool.h> typedef struct { int x; int y; } Location; typedef struct { bool walkable; unsigned char walked; // number of times walked upon } Cell; typedef struct { char name[40]; // Name of maze Cell **grid; // 2D array of cells int rows; // Number of rows int cols; // Number of columns Location entrance; } Maze; Maze *maz_new() { int i = 0; Maze *mazPtr = (Maze *)malloc(sizeof (Maze)); if(!mazPtr) { puts("The memory couldn't be initilised, Press ENTER to exit"); getchar(); exit(-1); } else { // allocating memory for the grid mazPtr->grid = (Cell **) malloc((sizeof (Cell)) * (mazPtr->rows)); for(i = 0; i < mazPtr->rows; i++) mazPtr->grid[i] = (Cell *) malloc((sizeof (Cell)) * (mazPtr->cols)); } return mazPtr; } void maz_delete(Maze *maz) { int i = 0; if (maz != NULL) { for(i = 0; i < maz->rows; i++) free(maz->grid[i]); free(maz->grid); } } int main() { Maze *ptr = maz_new(); maz_delete(ptr); getchar(); return 0; } Thanks in advance.

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  • Potential problem with C standard malloc'ing chars.

    - by paxdiablo
    When answering a comment to another answer of mine here, I found what I think may be a hole in the C standard (c1x, I haven't checked the earlier ones and yes, I know it's incredibly unlikely that I alone among all the planet's inhabitants have found a bug in the standard). Information follows: Section 6.5.3.4 ("The sizeof operator") para 2 states "The sizeof operator yields the size (in bytes) of its operand". Para 3 of that section states: "When applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1". Section 7.20.3.3 describes void *malloc(size_t sz) but all it says is "The malloc function allocates space for an object whose size is specified by size and whose value is indeterminate". It makes no mention at all what units are used for the argument. Annex E startes the 8 is the minimum value for CHAR_BIT so chars can be more than one byte in length. My question is simply this: In an environment where a char is 16 bits wide, will malloc(10 * sizeof(char)) allocate 10 chars (20 bytes) or 10 bytes? Point 1 above seems to indicate the former, point 2 indicates the latter. Anyone with more C-standard-fu than me have an answer for this?

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  • Unusual heap size limitations in VS2003 C++

    - by Shane MacLaughlin
    I have a C++ app that uses large arrays of data, and have noticed while testing that it is running out of memory, while there is still plenty of memory available. I have reduced the code to a sample test case as follows; void MemTest() { size_t Size = 500*1024*1024; // 512mb if (Size > _HEAP_MAXREQ) TRACE("Invalid Size"); void * mem = malloc(Size); if (mem == NULL) TRACE("allocation failed"); } If I create a new MFC project, include this function, and run it from InitInstance, it works fine in debug mode (memory allocated as expected), yet fails in release mode (malloc returns NULL). Single stepping through release into the C run times, my function gets inlined I get the following // malloc.c void * __cdecl _malloc_base (size_t size) { void *res = _nh_malloc_base(size, _newmode); RTCCALLBACK(_RTC_Allocate_hook, (res, size, 0)); return res; } Calling _nh_malloc_base void * __cdecl _nh_malloc_base (size_t size, int nhFlag) { void * pvReturn; // validate size if (size > _HEAP_MAXREQ) return NULL; ' ' And (size _HEAP_MAXREQ) returns true and hence my memory doesn't get allocated. Putting a watch on size comes back with the exptected 512MB, which suggests the program is linking into a different run-time library with a much smaller _HEAP_MAXREQ. Grepping the VC++ folders for _HEAP_MAXREQ shows the expected 0xFFFFFFE0, so I can't figure out what is happening here. Anyone know of any CRT changes or versions that would cause this problem, or am I missing something way more obvious?

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  • stack dump accessing malloc char array

    - by robUK
    Hello, gcc 4.4.3 c89 I have the following source code. And getting a stack dump on the printf. char **devices; devices = malloc(10 * sizeof(char*)); strcpy(devices[0], "smxxxx1"); printf("[ %s ]\n", devices[0]); /* Stack dump trying to print */ I am thinking that this should create an char array like this. devices[0] devices[1] devices[2] devices[4] etc And each element I can store my strings. Many thanks for any suggestions,

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  • Time taken for memcpy decreases after certain point

    - by tss
    I ve a code which increases the size of the memory(identified by a pointer) exponentially. Instead of realloc, I use malloc followed by memcpy.. Something like this.. int size=5,newsize; int *c = malloc(size*sizeof(int)); int *temp; while(1) { newsize=2*size; //begin time temp=malloc(newsize*sizeof(int)); memcpy(temp,c,size*sizeof(int)); //end time //print time in mili seconds c=temp; size=newsize; } Thus the number of bytes getting copied is increasing exponentially. The time required for this task also increases almost linearly with the increase in size. However after certain point, the time taken abruptly reduces to a very small value and then remains constant. I recorded time for similar code, copyin data(Of my own type) 5 -> 10 - 2 ms 10 -> 20 - 2 ms . . 2560 -> 5120 - 5 ms . . 20480 -> 40960 - 30 ms 40960 -> 91920 - 58 ms 367680 -> 735360 - 2 ms 735360 -> 1470720 - 2 ms 1470720 -> 2941440 - 2 ms What is the reason for this drop in time ? Does a more optimal memcpy method get called when the size is large ?

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  • Bug in malloc or mine?

    - by Martin
    Is this my bug or a bug/assertion fail in malloc itself? alloc.c:2451: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)-bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) = (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)-size & 0x1) && ((unsigned long)old_end & pagemask) == 0)' failed. libstdc++6:amd64 4.7.2-2ubuntu1 gcc 4.7.2 ubuntu 12.10/64bit

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  • Same memory space being allocated again & again while using malloc()

    - 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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  • x86 linux - how to create custom malloc with address hint

    - by nandu
    Hi, I want to create a custom malloc which allocates memory blocks within a given address range. I am writing a pthreads application in which threads are bound to unique cores on a many-core machine. The memory controllers are statically mapped, so that certain range of addresses on main memory are electrically closer to a core. I want to minimize the latency of communication between cores and main memory by allocating thread memory on these "closer" regions. Any ideas would be most appreciated. Thank you! Nandu

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  • malloc unable to assign memory + doesnt warn

    - by sraddhaj
    char *str=NULL; strsave(s,str,n+1); printf("%s",str-n); when I gdb debug this code I find that the str value is 0x0 which is null and also that my code is not catching this failed memory allocation , it doesnt execute str==NULL perror code ...Any idea void strsave(char *s,char *str,int n) { str=(char *)malloc(sizeof(char)* n); if(str==NULL) perror("failed to allocate memory"); while(*s) { *str++=*s++; } *str='\0'; }

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  • pointer and malloc [closed]

    - by gcc
    How many methods/ways are there taking input by using with pointer and dynamic memory? Input: 3 1 2 n k l 2 1 2 p 4 55 62 * # x (x is stop value, first input always integer) Example code: p=malloc(sizeof(int)); scanf("%d",&num_arrays); while(1) { scanf("%c",&(*(p+i))); if(*(p+i)=='x') break; ++i; } "3" is stored in num_arrays. The other input values are stored in pointer[array].

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  • I have a Segmentation fault (core dumped) when using strcpy, malloc, and struct

    - by malsh002
    Okay, when I run this code, I have a segmentation fault #include<stdio.h> #include<stdlib.h> #include<string.h> #define MAX 64 struct example { char *name; }; int main() { struct example *s = malloc (MAX); strcpy(s->name ,"Hello World!!"); return !printf("%s\n", s->name); } the terminal output: alshamlan@alshamlan-VGN-CR520E:/tmp/interview$ make q1 cc -Wall -g q1.c -o q1 alshamlan@alshamlan-VGN-CR520E:/tmp/interview$ ./q1 Segmentation fault (core dumped) alshamlan@alshamlan-VGN-CR520E:/tmp/interview$ gedit q1.c Can someone explain what's going on? thanks.

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  • Generating 2-dimensional vla ends in segmentation fault

    - by Framester
    Hi, further developing the code from yesterday (seg fault caused by malloc and sscanf in a function), I tried with the help of some tutorials I found on the net to generate a 2-dim vla. But I get a segmentation fault at (*data)[i][j]=atof(p);. The program is supposed to read a matrix out of a text file and load it into a 2d array (cols 1-9) and a 1D array (col 10) [Example code] #include<stdio.h> #include<stdlib.h> #include<math.h> #include<string.h> const int LENGTH = 1024; void read_data(float ***data, int **classes, int *nrow,int *ncol, char *filename){ FILE *pfile = NULL; char line[LENGTH]; if(!( pfile=fopen(filename,"r"))){ printf("Error opening %s.", filename); exit(1); } int numlines=0; int numcols=0; char *p; fgets(line,LENGTH,pfile); p = strtok (line," "); while (p != NULL){ p = strtok (NULL, ", "); numcols++; } while(fgets(line,LENGTH,pfile)){ numlines++; } rewind(pfile); int numfeats=numcols-1; *data=(float**) malloc(numlines*sizeof(float*)); *classes=(int *)malloc(numlines*sizeof(int)); if(*classes == NULL){ printf("\nOut of memory."); exit(1); } int i=0; while(fgets(line,LENGTH,pfile)){ p = strtok (line," "); for(int j=0;j<numfeats;j++) { (data)[i]=malloc(numfeats*sizeof(float)); printf("%i ",i); (*data)[i][j]=atof(p); p = strtok (NULL, ", "); } (*classes)[i]=atoi(p); i++; } fclose(pfile); *nrow=numlines; *ncol=numfeats; } int main() { char *filename="somedatafile.txt"; float **data2; int *classes2; int r,c; read_data(&data2,&classes2, &r, &c,filename) ; for(int i=0;i<r;i++){ printf("\n"); for(int j=0;j<c;j++){ printf("%f",data2[i][j]); } } return 1; } [Content of somedatafile.txt] 50 21 77 0 28 0 27 48 22 2 55 0 92 0 0 26 36 92 56 4 53 0 82 0 52 -5 29 30 2 1 37 0 76 0 28 18 40 48 8 1 37 0 79 0 34 -26 43 46 2 1 85 0 88 -4 6 1 3 83 80 5 56 0 81 0 -4 11 25 86 62 4 55 -1 95 -3 54 -4 40 41 2 1 53 8 77 0 28 0 23 48 24 4 37 0 101 -7 28 0 64 73 8 1 ...

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  • Tying in to Django Admin's Model History

    - by akdom
    The Setup: I'm working on a Django application which allows users to create an object in the database and then go back and edit it as much as they desire. Django's admin site keeps a history of the changes made to objects through the admin site. The Question: How do I hook my application in to the admin site's change history so that I can see the history of changes users make to their "content" ?

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  • Editing history in bash

    - by nameanyone
    In bash, when I go back in history, edit some command and run it, this edited command is appended to history and the original one is left intact. But every once in a while I somehow manage to affect the original command, i.e. my edit replaces the original command back in history. I can't put my finger on how this happens. Can someone explain? My goal is to avoid this, so any edit to a previous command always gets appended to history and never replaces the original.

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  • How to remove "Server name" items from history of SQL Server Management Studio

    - by arsenalogy
    When trying to connect to a server in Management Studio (specifically 2008), there is a field where you enter the Server name. That field also has a drop-down list where it shows a history of servers that you have attempted to connect to. I would like to know: How to remove an individual item from that history. How to remove an item from the Login field history for each Server name. Thanks!

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  • emacs: force ido-mode to forget history...

    - by Stephen
    Hi, I wonder if I can keep ido from not remembering my history and only show completions for files that are in the current directory when I am searching for a file. I understand that this history feature is useful at times, but I often end up editing the incorrect file because I think I am editing file called 'abc.txt' in the current directory but in fact I am editing the file by the same name in another one that I previously visited (often happens when there is not an 'abc.txt' in the current directory, as I mistakenly assume). From reading the ido.el file I thought to set in my .emacs file (also evaluated these expressions in running emacs instance): (custom-set-variables '(ido-enable-last-directory-history nil) '(ido-record-commands nil) ) and deleted a file called .ido.last in ~/, but still it remembers some previous files I've visited before making these changes. How can I purge my previous history, and I am not entirely sure what the difference between the two variables above are but seems to have done the trick to keep ido from remembering files I visit in the future? Thanks for your help!

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  • Open working copy file from eclipse history view

    - by Wolfgang
    The history view of eclipse shows you a list of files changed in a certain revision. When you open the context menu on one of these you have the option 'Open' which opens a view of that file in that revision. How can I open the editor for the selected file, i.e. the file in the version of the working copy, right from the history view? Background is that I want to use the history view to find files that have been changed recently to do code reviewing. People commit via subversion and I use subclipse to connect eclipse to the subversion server. Today, I must use the 'Open resource'/'Open type' function and type the name of the file that I can read from the history view.

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