memcmp

Precondition : Consider such a class or struct T , that for two objects a and b of type T memcmp(&a, &b, sizeof(T)) == 0 yields the same result as a.member1 == b.member1 && a.member2 == b.member2 && ... ( memberN is a non-static member variable of T ). Question : When should memcmp be used to compare a and b for equality, and when should the chained == s be used? Here's a simple example: struct vector { int x, y; }; To overload operator == for vector , there are two possibilities (if they're guaranteed to give the same result): bool operator==(vector lhs, vector rhs) { return lhs.x == rhs.x &&

This is a bit puzzling here. The following code is part of a little testing application to verify that code changes didn't introduce a regression. To make it fast we used memcmp which appears to be the fastest way of comparing two images of equal size (unsurprisingly). However, we have a few test images that exhibit a rather surprising problem: memcmp on the bitmap data tells us that they are not equal, however, a pixel-by-pixel comparison doesn't find any difference at all. I was under the impression that when using LockBits on a Bitmap you get the actual raw bytes of the image. For a 24 bpp

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I mean, I malloc a segment of memory, maybe 1k maybe 20bytes.. assume the pointer is pMem How can I know the content pMem refered is all Zero or \0 . I know memcmp but the second parameter should another memory address... thanx 回答1: As others have already suggested you probably want memset or calloc . But if you actually do want to check if a memory area is all zero, you can compare it with itself but shifted by one. bool allZero = pMem[0] == '\0' && !memcmp(pMem, pMem + 1, length - 1); where length is the number of bytes you want to be zero

I have a visual studio 2012 c++ project. I recently uninstalled it and installed visual studio 2015 and upgraded the project. When i am building the project, getting error as shown below: Error LNK2019 unresolved external symbol _memcmp referenced in function Moreover i have not used anywhere in my code memcmp fucntion. I used the linker verbose function and could see below in output file: Found _memcmp Referenced in MyC++Project.obj Referenced in libcpmtd.lib(xstrcoll.obj) Loaded libvcruntimed.lib(__memcmp_.obj) Two questions here 1.even though i have not used memcmp in my code why i am

Why is memcmp(a, b, size) so much faster than: for(i = 0; i < nelements; i++) { if a[i] != b[i] return 0; } return 1; Is memcmp a CPU instruction or something? It must be pretty deep because I got a massive speedup using memcmp over the loop. memcmp is often implemented in assembly to take advantage of a number of architecture-specific features, which can make it much faster than a simple loop in C. As a "builtin" GCC supports memcmp (as well as a ton of other functions) as builtins . In some versions / configurations of GCC, a call to memcmp will be recognized as __builtin_memcmp . Instead of

#include <string.h> int memcmp(const void *buf1, const void *buf2, unsigned int count); 比较内存区域buf1和buf2的前count个字节。 头文件 #include <string.h>或#include<memory.h> 返回值 当buf1<buf2时，返回值<0 当buf1=buf2时，返回值=0 当buf1>buf2时，返回值>0 所以该函数的功能实现为： #include<stdio.h> #include<assert.h> int my_memcmp(char *str1,char *str2,int len) { assert(str1); assert(str2); while(len–) { while(*str1==*str2) { if(*str1==’\0’) return 0; str1++; str2++; } } if(*str1>*str2) return 1; if(*str1<*str2) return -1; } int main() { char *p=“adcc”; char *q=“bac”; printf("%d\n",my_memcmp(p,q,1)); return 0; } 来源： CSDN 作者： weixin_45096886 链接：