The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group


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


#include <string.h>

[CX] [Option Start] char *stpncpy(char *restrict s1, const char *restrict s2, size_t n); [Option End]

char *strncpy(char *restrict
s1, const char *restrict s2, size_t n);


For strncpy(): [CX] [Option Start]  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.1-2017 defers to the ISO C standard. [Option End]

The [CX] [Option Start] stpncpy() [Option End]  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.


[CX] [Option Start] 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]. [Option End]

The strncpy() function shall return s1.

No return values are reserved to indicate an error.


No errors are defined.

The following sections are informative.




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.






strcpy, wcsncpy

XBD <string.h>


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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