ENDPWENT(3POSIX)

🌸 ENDPWENT(3POSIX) — user database functions 💖

okay bestie, welcome to the POSIX Programmer's Manual 🫶 this is the ENDPWENT(3POSIX) page, and we're gonna talk about three little functions that literally just want to read the user database with you. no gatekeeping, no cap.

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✨ PROLOG ✨

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

so like… bestie, the Linux version of this might be doing its own thing, and sometimes the interface isn't even implemented on Linux at all. check the Linux man page if you're on Linux, fr fr. 🙈

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💅 NAME 💅

endpwent, getpwent, setpwent — user database functions

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🎀 SYNOPSIS 🎀

#include <pwd.h>

void endpwent(void);
struct passwd *getpwent(void);
void setpwent(void);

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🦋 DESCRIPTION 🦋

These functions shall retrieve information about users. that's the whole vibe. 👑

The getpwent() function shall return a pointer to a structure containing the broken-out fields of an entry in the user database. Each entry in the user database contains a passwd structure. If the user database is not already open, getpwent() shall open it and return a pointer to a passwd structure containing the first entry in the database. Thereafter, it shall return a pointer to a passwd structure containing the next entry in the user database. Successive calls can be used to search the entire user database. it's giving "one at a time, we're going down the list" energy 💖

If an end-of-file or an error is encountered on reading, getpwent() shall return a null pointer. yeah. null. done. 🫥

An implementation that provides extended security controls may impose further implementation-defined restrictions on accessing the user database. In particular, the system may deny the existence of some or all of the user database entries associated with users other than the caller. so like, if the system is being ✨mysterious✨ about other people's entries, that's allowed, and it can literally pretend they don't exist. not ghosting you, it's just implementation-defined. 💀

The setpwent() function shall rewind the user database so that the next getpwent() call returns the first entry, allowing repeated searches. it's the "bestie, go back to the top" button 🎀

The endpwent() function shall close the user database. that's it. that's the function. iconic. 💅

The setpwent() and endpwent() functions shall not change the setting of errno if successful. like, if it worked, errno stays exactly how it was, hands off. ✋

On error, the setpwent() and endpwent() functions shall set errno to indicate the error.

Since no value is returned by the setpwent() and endpwent() functions, an application wishing to check for error situations should set errno to 0, then call the function, then check errno. that's the whole ritual bestie: zero it, call it, check it. 🔍

These functions need not be thread-safe. so don't be shocked if things get messy across threads, that's just how it is. 😭

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🌈 RETURN VALUE 🌈

On successful completion, getpwent() shall return a pointer to a passwd structure. On end-of-file, getpwent() shall return a null pointer and shall not change the setting of errno. On error, getpwent() shall return a null pointer and errno shall be set to indicate the error.

The application shall not modify the structure to which the return value points, nor any storage areas pointed to by pointers within the structure. The returned pointer, and pointers within the structure, might be invalidated or the structure or the storage areas might be overwritten by a subsequent call to getpwuid(), getpwnam(), or getpwent(). The returned pointer, and pointers within the structure, might also be invalidated if the calling thread is terminated.

🚨 BESTIE LISTEN. do not touch that structure. do not edit it. do not hold onto it and assume it's yours forever. the next call to getpwuid(), getpwnam(), or getpwent() can overwrite it, and if your thread gets terminated, poof 💀 the pointer can be invalidated too. copy what you need, don't get attached. 🫶

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💜 ERRORS 💜

These functions may fail if:

• EINTR — A signal was caught during the operation.
• EIO — An I/O error has occurred.

In addition, getpwent() and setpwent() may fail if:

• EMFILE — All file descriptors available to the process are currently open.
• ENFILE — The maximum allowable number of files is currently open in the system.

The following sections are informative. so like, cute but optional reading, iykyk 💖

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⭐ EXAMPLES ⭐

🔎 Searching the User Database

The following example uses the getpwent() function to get successive entries in the user database, returning a pointer to a passwd structure that contains information about each user. The call to endpwent() closes the user database and cleans up.

#include <pwd.h>
#include <stdio.h>

void printname(uid_t uid)
{
    struct passwd *pwd;

    setpwent();
    while((pwd = getpwent()) != NULL) {
        if (pwd->pw_uid == uid) {
            printf("name=%s\n",pwd->pw_name);
            break;
        }
    }
    endpwent();
}

look at her go 😭 setpwent() rewinds, the loop walks every entry, getpwent() hands you the next one, and once we find the matching pw_uid we print the name and dip. then endpwent() cleans up. main character energy, periodt. ✨

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🌸 APPLICATION USAGE 🌸

These functions are provided due to their historical usage. Applications should avoid dependencies on fields in the password database, whether the database is a single file, or where in the file system name space the database resides. Applications should use getpwuid() whenever possible because it avoids these dependencies.

ngl bestie, these are here because history said so 📜 don't go building your whole app on top of assumptions about what's in the password database, or whether it's one file, or where it lives in the file system name space. just use getpwuid() when you can, it dodges all of that. 🎀

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🧚 RATIONALE 🧚

None.

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🎀 FUTURE DIRECTIONS 🎀

None.

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💖 SEE ALSO 💖

endgrent(), getlogin(), getpwnam(), getpwuid()

The Base Definitions volume of POSIX.1‐2017, <pwd.h>

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👑 COPYRIGHT 👑

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page bestie!! 🫶 brought to you by IEEE/The Open Group, 2017 ✨ thanks for reading, you ate that, go forth and getpwent() responsibly 💅🎀