Some common primitive system data types
| Type | Description |
| caddr_t | core address |
| clock_t | counter of clock ticks (process time) |
| comp_t | compressed clock ticks |
| dev_t | device numbers (major and minor) |
| fd_set | file descriptor sets |
| fpos_t | file position |
| gid_t | numeric group IDs |
| ino_t | i-node numbers |
| mode_t | file type, file creation mode |
| nlink_t | link counts for directory entries |
| off_t | file sizes and offsets (signed) (lseek) |
| pid_t | process IDs and process group IDs (signed) |
| ptrdiff_t | result of subtracting two pointers (signed) |
| rlim_t | resource limits |
| sig_atomic_t | data type that can be accessed atomically |
| sigset_t | signal set |
| size_t | sizes of objects (such as strings) (unsigned) |
| ssize_t | functions that return a count of bytes (signed) (read, write) |
| time_t | counter of seconds of calendar time |
| uid_t | numeric user IDs |
| wchar_t | can represent all distinct character codes |
来源：oschina
链接：https://my.oschina.net/u/919901/blog/267895