The variable e is a pointer to an array of n + 1 elements of type double. Using the dereference operator on e gives you the base-type of e which is ” array of n + 1 elements of type double“. The malloc call simply takes the base-type of e (explained above) and gets its … Read more
Your code is wrong. You are allocating space for a single pointer (malloc(sizeof(char*))), but no characters. You are overwriting your allocated space with all the strings, causing undefined behavior (in tihs particular case, corrupting malloc()‘s book-keeping data). You don’t need to allocate space for the pointer (res), it’s a local variable. You must allocate space … Read more
On Linux, malloc requests memory with sbrk() or mmap() – either way, your address space is expanded immediately, but Linux does not assign actual pages of physical memory until the first write to the page in question. You can see the address space expansion in the VIRT column, while the actual, physical memory usage in … Read more
Since the question was asked, a new function was standardized by C11: void *aligned_alloc(size_t alignment, size_t size); and it is available in glibc (not on windows as far as I know). It takes its arguments in the same order as memalign, the reverse of Microsoft’s _aligned_malloc, and uses the same free function as usual for … Read more
new and delete are C++ specific features. They didn’t exist in C. malloc is the old school C way to do things. Most of the time, you won’t need to use it in C++. malloc allocates uninitialized memory. The allocated memory has to be released with free. calloc is like malloc but initializes the allocated … Read more
99.9% likely that you have corrupted memory (over- or under-flowed a buffer, wrote to a pointer after it was freed, called free twice on the same pointer, etc.) Run your code under Valgrind to see where your program did something incorrect.
Presumably you mean heap from a memory allocation point of view, not from a data structure point of view (the term has multiple meanings). A very simple explanation is that the heap is the portion of memory where dynamically allocated memory resides (i.e. memory allocated via malloc). Memory allocated from the heap will remain allocated … Read more
In C++, you need to cast the return of malloc() char *foo = (char*)malloc(1);
This is actually a really hard, imponderable question. Pro (in favor of freeing everything before exit): no bugs or memory leaks later if code is rearranged no false positives from valgrind or memory leak checker no memory leaks if you’re running under a buggy OS, or no OS at all Con (just exit, don’t worry … Read more
One of the things you have to realise when dealing with O notation is that it is often very important to understand what n is. If the n is something related to something you can control (eg: the number of elements in a list you want sorted) then it makes sense to look hard at … Read more