Linux 上readdir 遍历文件夹按文件名排序
遍历文件夹发送数据，数据文件名按时间排序，使用readdir 遍历时，没有按照文件名排序。
2017-10-15-00-00-00
2017-10-15-01-00-00
2017-10-15-02-00-00
最常见是readdir函数：
DIR *dir;
struct dirent *ptr;
dir = opendir(path.c_str());
if(NULL == dir)
{
cout << "opendir is NULL" << endl;
return;
}
while( (ptr = readdir(dir))!=NULL)
{
printf("d_ino：%ld d_off:%ld d_name: %s\n", ptr->d_ino,ptr->d_off,ptr->d_name);
}
closedir(dir);读取/etc/rc.d/目录，输出为：
d_ino：1048669 d_off:856980470154123585 d_name: rc5.d
d_ino：1048663 d_off:884029283848728392 d_name: init.d
d_ino：1048670 d_off:999482920564082138 d_name: rc6.d
d_ino：1059943 d_off:1785792148764494467 d_name: rc
d_ino：1048667 d_off:1841410420704204566 d_name: rc3.d
d_ino：1048666 d_off:3298607144791816940 d_name: rc2.d
d_ino：1048664 d_off:4425734956780595784 d_name: rc0.d
d_ino：1059945 d_off:5016870134774381628 d_name: rc.sysinit
d_ino：1048668 d_off:5182623748018784402 d_name: rc4.d
d_ino：1048665 d_off:6942952852705976198 d_name: rc1.d
d_ino：1048658 d_off:8782171503806864933 d_name: .
d_ino：1059944 d_off:9057741989092678028 d_name: rc.local
d_ino：1048577 d_off:9223372036854775807 d_name: ..
未按照文件名排序。其中：
struct dirent *readdir(DIR *dirp);
struct dirent
{
long d_ino; /* inode number 索引节点号 */
off_t d_off; /* offset to this dirent 在目录文件中的偏移 */
unsigned short d_reclen; /* length of this d_name 文件名长 */
unsigned char d_type; /* the type of d_name 文件类型 */
char d_name [NAME_MAX+1]; /* file name (null-terminated) 文件名，最长255字符 */
}readdir函数按照在磁盘的索引顺序，d_off来排序，如果需要按照文件名d_name，需要遍历后将文件名保存，再次排序。
查阅得知：scandir 可以实现按照规则排序
#include
int scandir(const char *dirp, struct dirent ***namelist,
int (*filter)(const struct dirent *),
int (*compar)(const struct dirent **, const struct dirent **));
int alphasort(const void *a, const void *b);
int versionsort(const void *a, const void *b);
alphasort() and scandir() are specified in POSIX.1-2008, and are widely available. version-sort() is a GNU extension.
The functions scandir() and alphasort() are from 4.3BSD, and have been available under Linux since libc4.
使用scandir遍历文件夹：
struct dirent **namelist;
int n;
n = scandir(path.c_str(),&namelist,0,alphasort);
if(n < 0)
{
cout << "scandir return "<< n << endl;
}
else
{
int index=0;
while(index < n)
{
printf("d_ino：%ld d_off:%ld d_name: %s\n", namelist[index]->d_ino,namelist[index]->d_off,namelist[index]->d_name);
free(namelist[index]);
index++;
}
free(namelist);
}输出：
d_ino：1048658 d_off:8782171503806864933 d_name: .
d_ino：1048577 d_off:9223372036854775807 d_name: ..
d_ino：1048663 d_off:884029283848728392 d_name: init.d
d_ino：1059943 d_off:1785792148764494467 d_name: rc
d_ino：1059944 d_off:9057741989092678028 d_name: rc.local
d_ino：1059945 d_off:5016870134774381628 d_name: rc.sysinit
d_ino：1048664 d_off:4425734956780595784 d_name: rc0.d
d_ino：1048665 d_off:6942952852705976198 d_name: rc1.d
d_ino：1048666 d_off:3298607144791816940 d_name: rc2.d
d_ino：1048667 d_off:1841410420704204566 d_name: rc3.d
d_ino：1048668 d_off:5182623748018784402 d_name: rc4.d
d_ino：1048669 d_off:856980470154123585 d_name: rc5.d
d_ino：1048670 d_off:999482920564082138 d_name: rc6.d
scandir函数中可以直接调用排序函数，将遍历到的文件名按照顺序保存在队列中。记得在使用后释放资源。
scandir函数通过参数4 调用比较函数实现排序，可以自定义int (*compar)(const struct dirent , const struct dirent )) 已按照某种规则来实现排序。
[email protected]:snippets/2599886.git
https://code.csdn.net/snippets/2599886