linux读写大文件

#include <stdio.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main() {
    int fd = open("largefile.txt", O_RDONLY);
    if (fd == -1) {
        perror("open");
        return 1;
    }

    struct stat sb;
    if (fstat(fd, &sb) == -1) {
        perror("fstat");
        close(fd);
        return 1;
    }

    char *addr = mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
    if (addr == MAP_FAILED) {
        perror("mmap");
        close(fd);
        return 1;
    }

    // 处理文件内容
    for (off_t i = 0; i < sb.st_size; i++) {
        printf("%c", addr[i]);
    }

    if (munmap(addr, sb.st_size) == -1) {
        perror("munmap");
    }

    close(fd);
    return 0;
}

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

#define BUFFER_SIZE 8192

int main() {
    int fd = open("largefile.txt", O_WRONLY | O_CREAT | O_TRUNC, 0644);
    if (fd == -1) {
        perror("open");
        return 1;
    }

    char buffer[BUFFER_SIZE];
    for (int i = 0; i < BUFFER_SIZE; i++) {
        buffer[i] = 'A';
    }

    off_t offset = 0;
    while (1) {
        ssize_t written = write(fd, buffer, BUFFER_SIZE);
        if (written == -1) {
            perror("write");
            break;
        }
        offset += written;
        if (written < BUFFER_SIZE) {
            break;
        }
    }

    close(fd);
    return 0;
}