memcpy

问题 #define buffer 128 int main(){ char buf[buffer]=""; ifstream infile("/home/kevin/Music/test.mp3",ios::binary); infile.seekg(-buffer,ios::end); if(!infile || !infile.read(buf,buffer)){ cout<<"fail!"<<endl; } ID3v1 id3; cout<<sizeof(id3)<<endl; memcpy(&id3,buf,128); cout<<id3.header<<endl; } struct ID3v1{ char header[3]; char title[30]; char artist[30]; char album[30]; char year[4]; char comment[28]; bool zerobyte; bool track; bool genre; }; When I do the memcpy, it seems to be pushing too much

问题 #define buffer 128 int main(){ char buf[buffer]=""; ifstream infile("/home/kevin/Music/test.mp3",ios::binary); infile.seekg(-buffer,ios::end); if(!infile || !infile.read(buf,buffer)){ cout<<"fail!"<<endl; } ID3v1 id3; cout<<sizeof(id3)<<endl; memcpy(&id3,buf,128); cout<<id3.header<<endl; } struct ID3v1{ char header[3]; char title[30]; char artist[30]; char album[30]; char year[4]; char comment[28]; bool zerobyte; bool track; bool genre; }; When I do the memcpy, it seems to be pushing too much

问题 I have several variables of different types stored in a char array. Normally I would write them to the array this way: int a = 5; memcpy(offset, (char*)&a, sizeof(int)) However, memcpy doesn't work in OpenCL kernels. What would be the easiest way to do the same without this function? 回答1: You can easily enough provide mymemcpy void mymemcpy(unsigned char *dest, const unsigned char *src, size_t N) { size_t i; for(i=0;i<N;i++) dest[i] = src[i]; } However it's not very efficient because most

问题 My question is this: Suppose type T is trivially copyable....can "create" an instance of this type without calling a constructor....like so: #include <type_traits> #include <cstring> using T = int; // T can be any trivially copyable type T create(const T& other) { std::aligned_storage_t<sizeof(T),alignof(T)> my_T; std::memcpy(&my_T,&other,sizeof(T)); return *reinterpret_cast<T*>(&my_T); } Is this defined behavior, or can I only copy into an existing object of type T? 回答1: The rule, from

问题 Does calling memcpy on two different structures preserve the original data if the buffer size is sufficient? And is it defined to retrieve values of another data type with data of previous data type if their respective data types overlap? This should be similar for both c/cpp languages but I'm providing an example in cpp - #include <iostream> #include <cstring> using namespace std; struct A{ int a; char b[10]; }; struct B{ int ba; int bb; }; int main(){ B tmp; tmp.ba = 50; tmp.bb = 24; cout <

问题 int a = 10; int* pA = &a; long long b = 200; long long* pB = &b; memcpy (pB,pA,4); memcpy (pB+1,pA,4); cout<<"I'm a memcpy!: "<<*(pB)<<endl; I'm doing some tests with memcpy to teach myself how memory works. What I am trying to do is make b = to "1010". I can copy the value from a to b, but then I try to offset the memory by 1 byte and write another 10 but it doesn't work it only outputs "10". What would I need to do to get a value of 1010? 回答1: A few problems with your code as it stands: You

问题 I was thinking about solving this, but it's looking to be quite a task. If I take this one by myself, I'll likely write it several different ways and pick the best, so I thought I'd ask this question to see if there's a good library that solves this already or if anyone has thoughts/advice. void OffsetMemCpy(u8* pDest, u8* pSrc, u8 srcBitOffset, size size) { // Or something along these lines. srcBitOffset is 0-7, so the pSrc buffer // needs to be up to one byte longer than it would need to be

问题 I have a requirement in which i need to pass an empty array as a parameter to a function. And in this called function, i should be memcpy some data into the passed array. So i have written a small example which is same as my requirement. Below is its code: #include <stdio.h> #include <stdlib.h> void printArr(int *a) { int i; int *b=(int*)malloc(sizeof(int)*10); printf("\n\nEnter 10 lements:\n"); for(i=0;i<10;i++) scanf("%d",&b[i]); printf("\nContents of array b:\n"); for(i=0;i<10;i++) printf(

问题 Struct A { uint16_t len; uint8_t cnt; uint8_t unit; uint32_t seq; }; This struct A is serialized into a char * buf. If I want to deserialize the individual values eg: uint16_t len = 0; memcpy(&len, buf, sizeof(len)); or I can just do uint16_t len = (uint16_t) buf; Which one is better or are both the same? Also to deserialize the whole struct, if I just do A tmp; memcpy(&tmp, buf, sizeof(A)); Would this work fine or should I be worried about padding etc from the compiler? 回答1: When the data is