mmap,memcpy将文件从A复制到B

我正在尝试使用MMAP和MEMCPY将文件从A复制到B. 下面的代码正是如此,但是当我使用CMP来比较块时,它说“mem_copy.c dest不同:字节1,第1行,我不知道为什么。

int main(int argc, char **argv){ int sfd, dfd; char *src, *dest; struct stat s; /* SOURCE */ sfd = open("hello.c", O_RDONLY); fstat(sfd, &s); // st_size = blocksize printf("%d\n", (int)s.st_size); src = mmap(NULL, s.st_size, PROT_READ, MAP_PRIVATE, sfd, 0); /* DESTINATION */ dfd = open("dest", O_RDWR | O_CREAT, 0666); ftruncate(dfd, s.st_size; dest = mmap(NULL, s.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, dfd, 0); /* COPY */ memcpy(dest, src, s.st_size); munmap(src, s.st_size); munmap(dest, s.st_size); close(sfd); close(dfd); return 0; } 

得到它了。

 int main(int argc, char **argv){ int sfd, dfd; char *src, *dest; size_t filesize; /* SOURCE */ sfd = open("hello.c", O_RDONLY); filesize = lseek(sfd, 0, SEEK_END); src = mmap(NULL, filesize, PROT_READ, MAP_PRIVATE, sfd, 0); /* DESTINATION */ dfd = open("dest", O_RDWR | O_CREAT, 0666); ftruncate(dfd, filesize); dest = mmap(NULL, filesize, PROT_READ | PROT_WRITE, MAP_SHARED, dfd, 0); /* COPY */ memcpy(dest, src, filesize); munmap(src, filesize); munmap(dest, filesize); close(sfd); close(dfd); return 0; }