The following analysis applies only to glibc (based on the ptmalloc2 algorithm). There are certain options that seem helpful to return the freed memory back to the system: mallopt() (defined in malloc.h) does provide an option to set the trim threshold value using one of the parameter option M_TRIM_THRESHOLD, this indicates the minimum amount of … Read more
Actually, malloc() (and other C runtime heap functions) are module dependant, which means that if you call malloc() in code from one module (i.e. a DLL), then you should call free() within code of the same module or you could suffer some pretty bad heap corruption (and this has been well documented). Using HeapAlloc() with … Read more
Whenever you pass a parameter to a function, a copy is made, and the function works on that copy. So in your case, you are trying to free a copy of the original object, which doesn’t make any sense. You should modify your function to take a pointer, and then you can have it call … Read more
First, you need to allocate array of pointers like char **c = malloc( N * sizeof( char* )), then allocate each row with a separate call to malloc, probably in the loop: /* N is the number of rows */ /* note: c is char** */ if (( c = malloc( N*sizeof( char* ))) == … Read more
No, there is no way to get this information without depending strongly on the implementation details of malloc. In particular, malloc may allocate more bytes than you request (e.g. for efficiency in a particular memory architecture). It would be much better to redesign your code so that you keep track of n explicitly. The alternative … Read more
When you malloc a block, it actually allocates a bit more memory than you asked for. This extra memory is used to store information such as the size of the allocated block, and a link to the next free/used block in a chain of blocks, and sometimes some “guard data” that helps the system to … Read more
In C++, you need to cast the return of malloc() char *foo = (char*)malloc(1);
Linux does deferred page allocation, aka. ‘optimistic memory allocation’. The memory you get back from malloc is not backed by anything and when you touch it you may actually get an OOM condition (if there is no swap space for the page you request), in which case a process is unceremoniously terminated. See for example … Read more
There are several different pieces at play here. The first is the difference between declaring an array as int array[n]; and int* array = malloc(n * sizeof(int)); In the first version, you are declaring an object with automatic storage duration. This means that the array lives only as long as the function that calls it … Read more
It depends upon requirement of your program. If your program has more dynamic memory allocations, then you need to choose a memory allocator, from available allocators, which would generate most optimal performance out of your program. For good memory management you need to meet the following requirements at minimum: Check if your system has enough … Read more