一、常见的文件操作相关的系统调用
二、st_mode 标志
三、文件状态结构体 stat
struct stat {dev_t st_dev; //文件的设备编号ino_t st_ino; //节点mode_t st_mode;//文件的类型和存取的权限nlink_t st_nlink;//连到该文件的硬连接数目，刚建立的文件值为1uid_t st_uid; //用户IDgid_t st_gid; //组IDdev_t st_rdev;//(设备类型)若此文件为设备文件，则为其设备编号off_t st_size;//文件字节数(文件大小)unsigned long st_blksize; //块大小(文件系统的I/O 缓冲区大小)unsigned long st_blocks; //块数time_t st_atime;//最后一次访问时间time_t st_mtime;//最后一次修改时间time_t st_ctime;//最后一次改变时间(指属性)};
读取文件时，可以获取文件的文件属性， 可以用以下三种方法
int stat(const char *file_name ,struct stat *buf) 按文件名获得文件的stat信息，如果时链接文件获取链接文件所指向的文件信息
int fstat(int filedes ,struct stat *buf) 和stat函数效果一样，只不过传入的参数时文件描述符
int lstat(const char *file_name ,struct stat *buf) 按文件名获得文件的stat信息，如果时链接文件获取文件本身的信息
下面展示linux 命令 ls 原理的程序：（不支持通配符）
open () 方法是打开文件,遵循符号链接，但是如果想打开文件内容本身，应调用
int readlink(char * pathname ,char buf[] , int bufsize);
/*************myls.c********************/#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/stat.h>#include <time.h>#include <sys/types.h>#include <dirent.h>#include <unistd.h>struct stat mystat,*sp;char *t1 = "xwrxwrxwr-------";char *t2 = "----------------";int ls_file(char *fname){struct stat fstat ,*sp;int r,i;char ftime[64];sp =& fstat;if( (r = lstat(fname,&fstat)) <0 ){printf("can't stat %s\n",fname);exit(1);}if ( (sp->st_mode &0xF000) == 0x8000 ){// S_ISREGprintf("%c",'-');}else if ( (sp->st_mode &0xF000) == 0x4000 ){// S_ISDIRprintf("%c",'d');}else if ( (sp->st_mode &0xF000) == 0xA000 ){// S_ISLNKprintf("%c",'l');}for ( i =8 ; i>=0 ;i--){ if (sp->st_mode & (1 << i )){printf("%c",t1[i]);} else {printf("%c",t2[i]);}}printf("%4d ",sp->st_nlink);printf("%4d ",sp->st_gid);printf("%4d ",sp->st_uid);printf("%8d ",sp->st_size);//print time strcpy(ftime ,ctime(&sp->st_ctime));ftime[strlen(ftime) -1 ] =0;printf ("%s " , ftime);//print name printf ("%s",basename(fname));//if symbolic file , print symfile ->linknameif( (sp->st_mode &0xF000) ==0xA000){//uss readlink() to read linknamechar *linkname;readlink (fname , linkname,1024);printf(" -> %s" , linkname); //print linked name}printf("\n");}int ls_dir(char *dname){ struct dirent *ep ;DIR *dp = opendir(dname);if(!dp){printf("no such dir %s\n",dname);exit(1);}char newpath[1024];while( ep = readdir(dp)){strcpy(newpath,dname);strcat(newpath , ep ->d_name);ls_file(newpath);}}int main(int argc , char *argv[]){struct stat mystat, *sp =&mystat;int r ;char *filename , path[1024] ,cwd[256];filename = "./";if (argc >1){filename =argv[1];}if( r = lstat(filename,sp) < 0 ){printf("no such file %s\n",filename);}strcpy(path , filename);if(path[0] != '/'){//相对路径getcwd(cwd,256);strcpy(path,cwd); strcat(path ,"/");strcat(path , filename);}if(S_ISDIR(sp -> st_mode)){printf ("path : %s\n", path);ls_dir(path);}elsels_file(path);}
四、复制文件， cp -r [srcPath] [destPath]原理
案例分析：
1）src必须存在，dest如果不存在则需要创建
2）如果src 是一个文件，dest 是一个文件或目录。如果是目录则创建同名文件，如果是文件，则直接复制文件内容
3）如果src是一个目录，那么dest必须一定是一个目录，通过readdir遍历src目录下的文件和字目录，复制到dest中
4）如果src 和dest 是同名文件则不复制 ， 如果dest 是src的后代目录则不能复制，包括自身。
可以分3个层级来组织程序：
1）最底层:文件复制文件 cpf2f
2）中间层： 将文件复制到目录中 cpf2d ，判断dest目录存在，然后调用 1 步骤
3) 最高层: 目录复制到目录cp2d2, 通过readdur遍历src目录，如果成员是文件则调用步骤2），如果成员是目录则递归调用步骤 3）
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <libgen.h>#include <fcntl.h>// for stat syscalls#include <sys/stat.h>#include <unistd.h>// for opendir, readdir syscalls#include <sys/types.h>#include <dirent.h>// cp file to fileint cpf2f(char *src, char *dst){int fd, gd, n, r1, r2, mode;char buf[1024];struct stat st1, st2;r1 = lstat(src, &st1);if (r1 < 0){printf("src %s does not exist\n", src);return -1;}if (S_ISDIR(st1.st_mode)){printf("src %s is not a file\n", src);return -1;}r2 = lstat(dst, &st2);if (r2 == 0){ // dst existif (st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino){printf("Src %s and dst %s are the same file\n", src, dst);return -1;}}if (r2 < 0){ // dst not exist; src if a filemode = st1.st_mode;if (S_ISLNK(mode)){printf("%s is a symlink file ==> ", src);n = readlink(src, buf, 1024); buf[n] = 0;printf("%s\n", buf);// make a symbolic filesymlink(buf, dst);return 0;}}// dst not but src is NOT LNK OR dst exist: cp src to dstfd = open(src, O_RDONLY); gd = open(dst, O_WRONLY|O_CREAT|O_TRUNC, mode);while( (n=read(fd, buf, 1024)) )write(gd, buf, n);close(fd); close(gd);return 0;}int cpf2d(char *f1, char *f2){int n, r1, r2, size;char buf[1024], name[128], f3[128], temp[128];DIR *gd;struct stat st, st3;struct dirent *ep;printf("cpf2d: cp %s into %s\n", f1, f2);r2 = lstat(f2, &st);if (r2 < 0 || S_ISDIR(st.st_mode)==0){printf("no such dir %s\n", f2);return -1;}strcpy(f3, f2); strcat(f3, "/");strcat(f3, basename(f1));if (lstat(f3, &st) < 0){ // f2/basename(f1) does not existreturn cpf2f(f1, f3);}// f2/basename(f1) exists in f2/if (S_ISREG(st.st_mode) || S_ISLNK(st.st_mode))return cpf2f(f1, f3);else{printf("cpf2d but f1 is a DIR, can't be true\n");return cpf2d(f1, f3);}}int sameFile(char *f1, char *f2){struct stat st1, st2;stat(f1, &st1); stat(f2, &st2);if (st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino)return 1;return 0;}int checkdir(char *f1, char *f2){while(!sameFile(f1, "/")){if (sameFile(f1, f2))return 1;strcat(f2, "/..");}return 0;}//int checkDir(char *f1, char *f2)//{// char temp[128], t[128];// int r0, r1, r2;// struct stat st0, st1, st2;// //printf("checkdir: %s %s\n", f1, f2);//// r0 = stat("/", &st0);printf("r0=%d root DIR = (%x %ld)\n", r0, (int)st0.st_dev, (long)st0.st_ino);//// r1 = stat(f1, &st1);//// //printf("r1=%d st1=[%x %ld]\n", r1, (int)st1.st_dev, (long)st1.st_ino);// // strcpy(temp, f2); strcat(temp, "/..");// while (1){// //printf("%s ", temp);// // r2 = stat(temp, &st2);// //printf("r2=%d st2=[%x %ld]\n", r2, (int)st2.st_dev, (long)st2.st_ino);//// if (st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino){////printf("found a match\n");//return 1;// }//// if (st2.st_dev == st0.st_dev && st2.st_ino == st0.st_ino){////printf("reached /\n");// break;// }// strcat(temp, "/..");// }// return 0;//}int cpdir(char *f1, char *f2){int n, r1, r2, found;char buf[1024], name[128], dname[128], temp[128];char src[128], dst[128], f3[128];DIR *fd, *gd;struct dirent *ep;struct stat st1, st2, st3;fd = opendir(f1);while( (ep = readdir(fd)) ){if (strcmp(ep->d_name, ".")==0 || strcmp(ep->d_name, "..")==0)continue;strcpy(src, f1); strcat(src, "/"); strcat(src, ep->d_name);strcpy(dst, f2); strcat(dst, "/"); strcat(dst, ep->d_name);r1 = lstat(src, &st1);if (S_ISREG(st1.st_mode) || S_ISLNK(st1.st_mode)){printf("cpf2f: %s to %s\n", src, dst);cpf2d(src, f2);}if (S_ISDIR(st1.st_mode)){/******r = stat(dst, &st3);if (r<0)mkdir(dst, 0755);*******///printf("recursive cp dir %s to %s\n", src, dst); cpd2d(src, dst);}}closedir(fd);return 1;}// recursively cp dir into dir int cpd2d(char *f1, char *f2){int n, r1, r2, found;char buf[1024], name[128], dname[128], temp[128];char temp1[128], temp2[128];char src[128], dst[128], f3[128];DIR *fd, *gd;struct dirent *ep;struct stat st1, st2, st3;//printf("entering cpd2d : %s %s\n", f1, f2);printf("cpd2d: %s %s\n", f1, f2);// 1. if f1 not exist => error outr1 = lstat(f1, &st1);if (r1 < 0 || S_ISDIR(st1.st_mode)==0){printf("%s is not a dir\n", f1);return -1;}// check f2:r2 = lstat(f2, &st2);// 2. if f2 not exist => mkdir f2if (r2 < 0){ // f2 not existprintf("mkdir: %s\n", f2);r2 = mkdir(f2, 0755);if (r2<0){printf("DIR %s already exists\n", f2);}return cpdir(f1, f2);}// f2 exist case:r2 = stat(f2, &st2);// 3. f2 existed but NOT DIR ==> error outif (r2 >= 0 && S_ISDIR(st2.st_mode)==0){printf("%s is not a dir\n", f2);return -1;}// 4. if f1 and f2 are SAME ==> error outif (st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino){printf("can't cp DIR f1 to itself\n");return -1;}// 5. check f2 is NOT under f1: if so error out// from f2, stat f2/.., f2/../../ until /; check whether ANY of these is f1if (checkdir(f1, f2)){printf("%s is inside %s\n", f2, f1);return -1;}// f2 existed:if (r2 >=0 ){ // f2 exist and is DIR: check whether same as f1 basenamestrcpy(temp1, f1);strcpy(temp2, f2);if (strcmp(basename(temp1), basename(temp2))){ // NOT same namestrcpy(temp, f2); strcat(temp, "/");strcpy(temp1, f1);strcat(temp, basename(temp1)); // create DIR f2/basenem(f1)printf("mkdir: %s\n", temp);r2 = mkdir(temp, 0755);}printf("mkdir2 DIR %s already exists\n", temp);return cpdir(f1, temp);}// f2 exist but NOT same as basename of f1return cpdir(f1, f2);}int myrcp(char *f1, char *f2){struct stat st1, st2; int r1, r2, m1, m2, c;// MUST use lstat() because f1 may be a symlink filer1 = lstat(f1, &st1);if (r1 < 0){printf("no src file %s\n", f1);return -1;}m1 = st1.st_mode;if (!S_ISREG(m1) && !S_ISDIR(m1) && !S_ISLNK(m1)){printf("src is not REG, DIR or LNK file\n");exit(2);}r2 = lstat(f2, &st2);m2 = st2.st_mode;if (r2 < 0){ // f2 does NOT existif (S_ISREG(st1.st_mode) || S_ISLNK(st1.st_mode))return cpf2f(f1, f2);if (S_ISDIR(st1.st_mode))return cpd2d(f1, f2);}if (r2==0){ // f2 existsif (!S_ISREG(m1) && !S_ISDIR(m1) && !S_ISLNK(m1)){printf("dst %s is not REG, DIR or LNK file\n", f2);exit(2);}}if (r2 == 0){ // f2 exists; check whether f1 == f2if (st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino){printf("%s and %s are the same file\n", f1, f2);return -1;}}if (S_ISREG(m1) || S_ISLNK(m1)){if (S_ISREG(m2))return cpf2f(f1, f2);if (S_ISDIR(m2))return cpf2d(f1,f2);}printf("%s is not a file; try dir\n", f1);if (S_ISDIR(m1)){if (S_ISREG(m2)){printf("can't cp dir into file\n");return -1;}r2 = stat(f2, &st2);if (r2 < 0) // f2 does not exist yetmkdir(f2, 0755);r2 = stat(f2, &st2);m2 = st2.st_mode;if (S_ISDIR(m2)){printf("cp dir to dir\n");return cpd2d(f1, f2);}}}int main(int argc, char *argv[]){if (argc < 3){printf("Usage: rcp SRC DST\n");exit(1);}return myrcp(argv[1], argv[2]);}
