memory-management

问题 How can I get, given a pointer to a block of memory allocated with malloc, the size of it? For example: void* ptr = malloc( 10 ); //Allocate 10 bytes printf( "%d", GetMemSize( ptr ) ); //Should print 10 I want to do this for debugging purposes. 回答1: In Visual C++ you can use _msize() for that. 回答2: The Microsoft CRT has a function size_t _msize(void *memblock); which will give you the size of the allocated block. Note this may be (and in fact is likely to be) larger than the size asked for,

问题 i was going through pytorch tutorial and came across pytorch.empty function. it was mentioned that empty can be used for uninitialized data . But, when i printed it, i got a value. what is the difference between this and pytorch.rand which also generates data(i know that rand generates between 0 and 1). Below is the code i tried a = torch.empty(3,4) print(a) Output: tensor([[ 8.4135e-38, 0.0000e+00, 6.2579e-41, 5.4592e-39], [-5.6345e-08, 2.5353e+30, 5.0447e-44, 1.7020e-41], [ 1.4000e-38, 5

问题 i was going through pytorch tutorial and came across pytorch.empty function. it was mentioned that empty can be used for uninitialized data . But, when i printed it, i got a value. what is the difference between this and pytorch.rand which also generates data(i know that rand generates between 0 and 1). Below is the code i tried a = torch.empty(3,4) print(a) Output: tensor([[ 8.4135e-38, 0.0000e+00, 6.2579e-41, 5.4592e-39], [-5.6345e-08, 2.5353e+30, 5.0447e-44, 1.7020e-41], [ 1.4000e-38, 5

问题 Problem When experimenting with the JNI interface, I was wondering if I could take a JObject and transmute it into an equivalent struct to manipulate the fields. However, when I tried I was surprised to see that this did not work. Ignoring how horrible this idea might be, why didn't it work? My Approach Java Test Class I made a simple class Point to do my test. Point has two fields and a constructor that takes in an x and y as well as a few random methods that return information based on the

问题 A very basic question .. but really very important to understand the concepts.. in c++ or c languages, we usually don't use pointer variables to store values.. i.e. values are stored simply as is in: int a=10; but here in ios sdk, in objective c, most of the objects which we use are initialized by denoting a pointer with them as in: NSArray *myArray=[NSArray array]; So,the question arises in my mind ,that, what are the benefit and need of using pointer-objects (thats what we call them here,

问题 I have allocated heap memory in the thread function f1 , this storage is used to calculate the value in the heap region so that the main function can see it. Here is the thread function definition: void *f1(void *input){ int sum = (int*)malloc(sizeof(int)); /* Do calculation */ pthread_exit((void*)&sum); } In the above code, the sum is the heap allocated storage, whose address is passed as a return value to the sum1 in the main() . I join the thread in the main() like this: void *sum1;

问题 I have allocated heap memory in the thread function f1 , this storage is used to calculate the value in the heap region so that the main function can see it. Here is the thread function definition: void *f1(void *input){ int sum = (int*)malloc(sizeof(int)); /* Do calculation */ pthread_exit((void*)&sum); } In the above code, the sum is the heap allocated storage, whose address is passed as a return value to the sum1 in the main() . I join the thread in the main() like this: void *sum1;

问题 It would be efficient for some purposes to allocate a huge amount of virtual space, and page in only pages that are accessed. Allocating a large amount of memory is instantaneous and does not actually grab pages: char* p = new char[1024*1024*1024*256]; Ok, the above was wrong as pointed out because it's a 32 bit number. I expect that new is calling malloc which calls sbrk, and that when I access a location 4Gb beyond the start, it tries to extend the task memory by that much? Here is the full

问题 I have simple messages: message SmallValue { int32 val = 1; } message Value { int32 val1 = 1; int32 val2 = 2; SmallValue val3 = 3; } message SendMessage { int32 id = 1; oneof message { Value value= 2; } My piece of code: // create new pointer for smallValue SmallValue* smallValue = new SmallValue(); smallValue->set_val3(3); // create new object value and set_allocated_val3 Value value; value.set_val1(1); value.set_val2(2); value.set_allocated_val3(smallValue); // create new object message and

问题 I saw from the documentation of userfaultfd https://manpages.debian.org/testing/manpages-dev/userfaultfd.2.en.html http://man7.org/linux/man-pages/man2/ioctl_userfaultfd.2.html that userfaultfd will start supporting shared map since kernel 4.11. However, the documentation still looks very ambiguous in the sense that I'm still wondering will these include supporting file-backed mmap (which can also be MAP_SHARED)? 回答1: To answer definitively, since the information is not in the manual page(s),