C語言 如何知道檔案大小

1.利用fseek(或lseek)

FILE* f = fopen(fileName, "r+");
fseek(f, 0, SEEK_END);
size = ftell(f);
fseek(f, 0, SEEK_SET);

2.用stat函式

struct stat st;
stat(fileName, &st);
size = st.st_size;

其中stat結構如下

struct stat {
    dev_t     st_dev;     /* ID of device containing file */
    ino_t     st_ino;     /* inode number */
    mode_t    st_mode;    /* protection */
    nlink_t   st_nlink;   /* number of hard links */
    uid_t     st_uid;     /* user ID of owner */
    gid_t     st_gid;     /* group ID of owner */
    dev_t     st_rdev;    /* device ID (if special file) */
    off_t     st_size;    /* total size, in bytes */
    blksize_t st_blksize; /* blocksize for file system I/O */
    blkcnt_t  st_blocks;  /* number of 512B blocks allocated */
    time_t    st_atime;   /* time of last access */
    time_t    st_mtime;   /* time of last modification */
    time_t    st_ctime;   /* time of last status change */
};

參考至man page (2)