Shulou(Shulou.com)06/01 Report--

This article mainly introduces what are the memory functions in C language, which can be used for reference. I hope you can learn a lot after reading this article.

Memory function 1. Copy memcpy,memmove

Void * memcpy (void * destination, const void * source, size_t num)

Dest replicates num bytes of data in src.

Simulation and implementation of memcpy

Void * my_memcpy (void * dst, const void * src, size_t count) {void * ret = dst; while (count--) {* (char *) dst = * (char *) src; dst = (char *) dst + 1; src = (char *) src + 1;} return (ret);}

What happens if dst and src point to the same array?

Int main () {int arr1 [10] = {1 int arr1 [10] = {1 int I = 0; / / expected results 1 2 1 2 3 4 7 8 9 0 my_memcpy (arr1+2, arr1, 16); for (int I = 0; I

< 10; i++) { printf("%d ", arr1[i]); }} 实际为 1 2 1 2 1 2 7 8 9 0 因为到5 6 的时候3 4被改成了1 2 ，5 6也就被改成1 2。 也就是说被复制的元素在复制前被改变了，导致复制结果失败。 如果是这样指向同一个数组呢？ int main(){ int arr1[10] = { 1,2,3,4,5,6,7,8,9,0 }; my_memcpy(arr1, arr1+2, 16); for (int i = 0; i < 10; i++) { printf("%d ", arr1[i]); }} 复制结果没有问题。 对于这种情况，c语言有一个更强大的函数memmove. void * memmove( void * destination, const void * source, size_t num ); 与memcpy的功能一样，但是memmove可以指向同一块空间。 模拟实现memmove **void* my_memmove(void* dest, void* src, size_t num){ char* ret = dest; //如果指向同一块空间 判断地址大小，避免数据在被复制前被改变 if ( (char*)dest-(char*)src< 0){ while (num) { *((char*)dest)++ = *((char*)src)++; num--; } } else { while(num--){ *((char*)dest+num) = *((char*)src+num); } } return ret;}2.比较 memcmp int memcmp ( const void * ptr1, const void * ptr2, size_t num ); 从ptr1和ptr2的位置开始比较num个字节，当两个字节数据不同时就会返回。 ptr1>

Ptr2 return value > 0

Ptr1=ptr2 return value = 0

Ptr1

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