The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> stpncpy, strncpy - copy fixed length string, returning a pointer to the array end

#### SYNOPSIS

> ``#include <string.h>
> ``

> ``[CX] char *stpncpy(char *restrict` s1`, const char *restrict` s2`, size_t` n`);``
> `
> char *strncpy(char *restrict` s1`, const char *restrict` s2`, size_t` n`);
> `

#### DESCRIPTION

> For strncpy(): [CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

> The [CX] stpncpy() and strncpy() functions shall copy not more than n bytes (bytes that follow a NUL character are not copied) from the array pointed to by s2 to the array pointed to by s1.

> If the array pointed to by s2 is a string that is shorter than n bytes, NUL characters shall be appended to the copy in the array pointed to by s1, until n bytes in all are written.

> If copying takes place between objects that overlap, the behavior is undefined.

#### RETURN VALUE

> [CX] If a NUL character is written to the destination, the stpncpy() function shall return the address of the first such NUL character. Otherwise, it shall return &s1[n].

> The strncpy() function shall return s1.

> No return values are reserved to indicate an error.

#### ERRORS

> No errors are defined.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> Applications must provide the space in s1 for the n bytes to be transferred, as well as ensure that the s2 and s1 arrays do not overlap.

> Character movement is performed differently in different implementations. Thus, overlapping moves may yield surprises.

> If there is no NUL character byte in the first n bytes of the array pointed to by s2, the result is not null-terminated.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> strcpy, wcsncpy

> XBD <string.h>

#### CHANGE HISTORY

> First released in Issue 1. Derived from Issue 1 of the SVID.

#### Issue 6

> The strncpy() prototype is updated for alignment with the ISO/IEC 9899:1999 standard.

#### Issue 7

> The stpncpy() function is added from The Open Group Technical Standard, 2006, Extended API Set Part 1.

End of informative text.

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