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Full Discussion: find size of heap allocated
Top Forums Programming find size of heap allocated Post 302520044 by Loic Domaigne on Thursday 5th of May 2011 04:21:02 PM
Old 05-05-2011
Quote:
Originally Posted by rupeshkp728
I want to find the size of the total memory allocated on the heap for the following statement:
int* a = new int[1000];How can I use the sizeof operator for this?
I used:
printf("\t===> %d\n",sizeof(*a));

Is this statement correct?

I have asked the question because when I checked the memory of heap allocated in windbg it shows me the size as fc4 i.e. 4036 which is more then 4000 and not as desired. Any hint as to what may be the cause?
The statement is not correct, you'll get the size of an int on your architecture.

windbg... hmm... that's doesn't sound really Un*x...

Remember that new[] is an operator provided by your compiler, we don't know what it does... It may for instance add a header for internal bookkeeping; or perhaps the underlying allocation mechanism on your system imposed this... Who knows?

You'll have to look at the interna of the new[] operator to find it out.

Cheers, Loïc
 

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MALLOC_INFO(3)						     Linux Programmer's Manual						    MALLOC_INFO(3)

NAME
malloc_info - export malloc state to a stream SYNOPSIS
#include <malloc.h> int malloc_info(int options, FILE *stream); DESCRIPTION
The malloc_info() function exports an XML string that describes the current state of the memory-allocation implementation in the caller. The string is printed on the file stream stream. The exported string includes information about all arenas (see malloc(3)). As currently implemented, options must be zero. RETURN VALUE
On success, malloc_info() returns 0; on error, it returns -1, with errno set to indicate the cause. ERRORS
EINVAL options was nonzero. VERSIONS
malloc_info() was added to glibc in version 2.10. CONFORMING TO
This function is a GNU extension. NOTES
The memory-allocation information is provided as an XML string (rather than a C structure) because the information may change over time (according to changes in the underlying implementation). The output XML string includes a version field. The open_memstream(3) function can be used to send the output of malloc_info() directly into a buffer in memory, rather than to a file. The malloc_info() function is designed to address deficiencies in malloc_stats(3) and mallinfo(3). EXAMPLE
The program below takes up to four command-line arguments, of which the first three are mandatory. The first argument specifies the number of threads that the program should create. All of the threads, including the main thread, allocate the number of blocks of memory speci- fied by the second argument. The third argument controls the size of the blocks to be allocated. The main thread creates blocks of this size, the second thread created by the program allocates blocks of twice this size, the third thread allocates blocks of three times this size, and so on. The program calls malloc_info() twice to display the memory-allocation state. The first call takes place before any threads are created or memory allocated. The second call is performed after all threads have allocated memory. In the following example, the command-line arguments specify the creation of one additional thread, and both the main thread and the addi- tional thread allocate 10000 blocks of memory. After the blocks of memory have been allocated, malloc_info() shows the state of two allo- cation arenas. $ getconf GNU_LIBC_VERSION glibc 2.13 $ ./a.out 1 10000 100 ============ Before allocating blocks ============ <malloc version="1"> <heap nr="0"> <sizes> </sizes> <total type="fast" count="0" size="0"/> <total type="rest" count="0" size="0"/> <system type="current" size="135168"/> <system type="max" size="135168"/> <aspace type="total" size="135168"/> <aspace type="mprotect" size="135168"/> </heap> <total type="fast" count="0" size="0"/> <total type="rest" count="0" size="0"/> <system type="current" size="135168"/> <system type="max" size="135168"/> <aspace type="total" size="135168"/> <aspace type="mprotect" size="135168"/> </malloc> ============ After allocating blocks ============ <malloc version="1"> <heap nr="0"> <sizes> </sizes> <total type="fast" count="0" size="0"/> <total type="rest" count="0" size="0"/> <system type="current" size="1081344"/> <system type="max" size="1081344"/> <aspace type="total" size="1081344"/> <aspace type="mprotect" size="1081344"/> </heap> <heap nr="1"> <sizes> </sizes> <total type="fast" count="0" size="0"/> <total type="rest" count="0" size="0"/> <system type="current" size="1032192"/> <system type="max" size="1032192"/> <aspace type="total" size="1032192"/> <aspace type="mprotect" size="1032192"/> </heap> <total type="fast" count="0" size="0"/> <total type="rest" count="0" size="0"/> <system type="current" size="2113536"/> <system type="max" size="2113536"/> <aspace type="total" size="2113536"/> <aspace type="mprotect" size="2113536"/> </malloc> Program source #include <unistd.h> #include <stdlib.h> #include <pthread.h> #include <malloc.h> #include <errno.h> static size_t blockSize; static int numThreads, numBlocks; #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); } while(0) static void * thread_func(void *arg) { int j; int tn = (int) arg; /* The multiplier '(2 + tn)' ensures that each thread (including the main thread) allocates a different amount of memory */ for (j = 0; j < numBlocks; j++) if (malloc(blockSize * (2 + tn)) == NULL) errExit("malloc-thread"); sleep(100); /* Sleep until main thread terminates */ return NULL; } int main(int argc, char *argv[]) { int j, tn, sleepTime; pthread_t *thr; if (argc < 4) { fprintf(stderr, "%s num-threads num-blocks block-size [sleep-time] ", argv[0]); exit(EXIT_FAILURE); } numThreads = atoi(argv[1]); numBlocks = atoi(argv[2]); blockSize = atoi(argv[3]); sleepTime = (argc > 4) ? atoi(argv[4]) : 0; thr = calloc(numThreads, sizeof(pthread_t)); if (thr == NULL) errExit("calloc"); printf("============ Before allocating blocks ============ "); malloc_info(0, stdout); /* Create threads that allocate different amounts of memory */ for (tn = 0; tn < numThreads; tn++) { errno = pthread_create(&thr[tn], NULL, thread_func, (void *) tn); if (errno != 0) errExit("pthread_create"); /* If we add a sleep interval after the start-up of each thread, the threads likely won't contend for malloc mutexes, and therefore additional arenas won't be allocated (see malloc(3)). */ if (sleepTime > 0) sleep(sleepTime); } /* The main thread also allocates some memory */ for (j = 0; j < numBlocks; j++) if (malloc(blockSize) == NULL) errExit("malloc"); sleep(2); /* Give all threads a chance to complete allocations */ printf(" ============ After allocating blocks ============ "); malloc_info(0, stdout); exit(EXIT_SUCCESS); } SEE ALSO
mallinfo(3), malloc(3), malloc_stats(3), mallopt(3), open_memstream(3) GNU
2015-01-22 MALLOC_INFO(3)
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