1.\" $NetBSD: reallocarray.3,v 1.2 2015/02/05 22:05:33 christos Exp $ 2.\" 3.Dd February 5, 2015 4.Dt REALLOCARRAY 3 5.Os 6.Sh NAME 7.Nm reallocarray 8.Nd reallocate memory for an array of elements checking for overflow 9.Sh SYNOPSIS 10.Vt #define _OPENBSD_SOURCE 11.In stdlib.h 12.Ft void * 13.Fo reallocarray 14.Fa "void *ptr" 15.Fa "size_t nmemb" 16.Fa "size_t size" 17.Fc 18.Sh DESCRIPTION 19The 20.Fn reallocarray 21function reallocates the pointer 22.Fa ptr 23to a size appropriate to handle an allocation of 24.Fa nmemb 25elements in an array where each of the array elements is 26.Fa size 27bytes using 28.Xr realloc 3 29and making sure that overflow does not happen in the multiplication of 30.Dq "nmemb * size" . 31.Pp 32This function is provided for source compatibility with 33.Ox 34and 35its use is discouraged in preference to 36.Xr reallocarr 3 . 37.Sh RETURN VALUES 38The 39.Fn reallocarray 40function will return 41.Dv NULL 42if there was overflow or if 43.Xr realloc 3 44failed setting 45.Va errno 46to 47.Dv EOVERFLOW 48or preserving the value from 49.Xr realloc 3 . 50.Sh SEE ALSO 51.Xr malloc 3 , 52.Xr realloc 3 , 53.Xr reallocarr 3 54.Sh STANDARDS 55.Fn reallocarray 56is an 57.Ox 58extension. 59.Sh HISTORY 60The 61.Fn reallocarray 62function first appeared in 63.Ox 5.6 . 64.Fn reallocarray 65was redesigned in 66.Nx 8 67as 68.Fn reallocarr 3 . 69For compatibility reasons it's available since 70.Nx 8 71in the 72.Vt _OPENBSD_SOURCE 73namespace. 74.Sh CAVEATS 75The 76.Fn reallocarray 77function was designed to facilitate safe, 78robust programming and overcome the shortcomings of the 79.Xr malloc 3 80and 81.Xr realloc 3 82functions by centralizing the overflow check in the multiplication of 83.Fa nmemb 84and 85.Fa size . 86.Pp 87There are still portability issues (it does not solve 88the 89.Dv 0 90sized allocation return ambiguity in the C standard: does 91.Fn reallocarray 92return 93.Dv NULL 94or a unique pointer to memory that cannot be accessed? Does a 95.Dv NULL 96mean that an error occurred, and can someone check 97.Dv errno 98in that case to find out what happened?). 99.Pp 100For this reason 101.Nx 102decided to go with an alternative implementation, and created 103.Xr reallocarr 3 . 104