#### 29.13.2 Looking Up One User

You can search the system user database for information about a specific user using `getpwuid` or `getpwnam`. These functions are declared in `pwd.h`.

— Function: struct passwd * getpwuid (uid_t uid)

> This function returns a pointer to a statically-allocated structure containing information about the user whose user ID is uid. This structure may be overwritten on subsequent calls to `getpwuid`.

> A null pointer value indicates there is no user in the data base with user ID uid.

— Function: int getpwuid_r (uid_t uid, struct passwd *result_buf, char *buffer, size_t buflen, struct passwd **result)

> This function is similar to `getpwuid` in that it returns information about the user whose user ID is uid. However, it fills the user supplied structure pointed to by result_buf with the information instead of using a static buffer. The first buflen bytes of the additional buffer pointed to by buffer are used to contain additional information, normally strings which are pointed to by the elements of the result structure.

> If a user with ID uid is found, the pointer returned in result points to the record which contains the wanted data (i.e., result contains the value result_buf). If no user is found or if an error occurred, the pointer returned in result is a null pointer. The function returns zero or an error code. If the buffer buffer is too small to contain all the needed information, the error code `ERANGE` is returned and errno is set to `ERANGE`.

— Function: struct passwd * getpwnam (const char *name)

> This function returns a pointer to a statically-allocated structure containing information about the user whose user name is name. This structure may be overwritten on subsequent calls to `getpwnam`.

> A null pointer return indicates there is no user named name.

— Function: int getpwnam_r (const char *name, struct passwd *result_buf, char *buffer, size_t buflen, struct passwd **result)

> This function is similar to `getpwnam` in that is returns information about the user whose user name is name. However, like `getpwuid_r`, it fills the user supplied buffers in result_buf and buffer with the information instead of using a static buffer.

> The return values are the same as for `getpwuid_r`.