写一份内存映射 I/O完整源码

下面是一份简单的内存映射 I/O 的完整源码：

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>

using namespace std;

int main(int argc, char* argv[]) {
    int fd;
    struct stat sb;
    off_t len;
    char *p;
    if (argc < 2) {
        cerr << "Usage: " << argv[0] << " <file>" << endl;
        exit(EXIT_FAILURE);
    }
    fd = open(argv[1], O_RDONLY);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }
    if (fstat(fd, &sb) == -1) {
        perror("fstat");
        exit(EXIT_FAILURE);
    }
    if (!S_ISREG(sb.st_mode)) {
        cerr << argv[1] << " is not a file" << endl;
        exit(EXIT_FAILURE);
    }
    p = (char*) mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
    if (p == MAP_FAILED) {
        perror("mmap");
        exit(EXIT_FAILURE);
    }
    if (close(fd) == -1) {
        perror("close");
        exit(EXIT_FAILURE);
    }
    for (len = 0; len < sb.st_size; len++) {
        putchar(p[len]);
    }
    if (munmap(p, sb.st_size) == -1) {
        perror("munmap");
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}

这份代码实现了将指定的文件进行内存映射，然后将文件内容输出到标准输出。具体实现细节可以参考代码注释。