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。

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