free

How does free know how much to free?

由 空扰寡人 提交于 2019-11-25 23:59:18
问题 In C programming, you can pass any kind of pointer you like as an argument to free, how does it know the size of the allocated memory to free? Whenever I pass a pointer to some function, I have to also pass the size (ie an array of 10 elements needs to receive 10 as a parameter to know the size of the array), but I do not have to pass the size to the free function. Why not, and can I use this same technique in my own functions to save me from needing to cart around the extra variable of the

What REALLY happens when you don't free after malloc?

由 早过忘川 提交于 2019-11-25 23:00:00
问题 This has been something that has bothered me for ages now. We are all taught in school (at least, I was) that you MUST free every pointer that is allocated. I\'m a bit curious, though, about the real cost of not freeing memory. In some obvious cases, like when malloc is called inside a loop or part of a thread execution, it\'s very important to free so there are no memory leaks. But consider the following two examples: First, if I have code that\'s something like this: int main() { char *a =

How do malloc() and free() work?

由 旧巷老猫 提交于 2019-11-25 22:23:46
问题 I want to know how malloc and free work. int main() { unsigned char *p = (unsigned char*)malloc(4*sizeof(unsigned char)); memset(p,0,4); strcpy((char*)p,\"abcdabcd\"); // **deliberately storing 8bytes** cout << p; free(p); // Obvious Crash, but I need how it works and why crash. cout << p; return 0; } I would be really grateful if the answer is in depth at memory level, if it\'s possible. 回答1: OK some answers about malloc were already posted. The more interesting part is how free works (and

How do free and malloc work in C?

由 北战南征 提交于 2019-11-25 20:40:29
I'm trying to figure out what would happened if I try to free a pointer "from the middle" for example, look at the following code: char *ptr = (char*)malloc(10*sizeof(char)); for (char i=0 ; i<10 ; ++i) { ptr[i] = i+10; } ++ptr; ++ptr; ++ptr; ++ptr; free(ptr); I get a crash with an Unhandled exception error msg. I want to understand why and how free works so that I know not only how to use it but also be able to understand weird errors and exceptions and better debug my codeץ Thanks a lot When you malloc a block, it actually allocates a bit more memory than you asked for. This extra memory is

Will malloc implementations return free-ed memory back to the system?

由 自作多情 提交于 2019-11-25 19:21:36
I have a long-living application with frequent memory allocation-deallocation. Will any malloc implementation return freed memory back to the system? What is, in this respect, the behavior of: ptmalloc 1, 2 (glibc default) or 3 dlmalloc tcmalloc (google threaded malloc) solaris 10-11 default malloc and mtmalloc FreeBSD 8 default malloc (jemalloc) Hoard malloc? Update If I have an application whose memory consumption can be very different in daytime and nighttime (e.g.), can I force any of malloc's to return freed memory to the system? Without such return freed memory will be swapped out and in
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