---
name: "BN_zero"
section: "3ssl"
platform: "linux"
package: "openssl"
version: "3.6.5-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/BN_zero"
---

# BN\_zero(3ssl)

BIGNUM assignment operations

## NAME

BN\_zero, BN\_one, BN\_value\_one, BN\_set\_word, BN\_get\_word - BIGNUM assignment operations

## SYNOPSIS

```
 #include <openssl/bn.h>
 void BN_zero(BIGNUM *a);
 int BN_one(BIGNUM *a);
 const BIGNUM *BN_value_one(void);
 int BN_set_word(BIGNUM *a, BN_ULONG w);
 unsigned BN_ULONG BN_get_word(BIGNUM *a);
```

## DESCRIPTION

**BN\_ULONG** is a macro that will be an unsigned integral type optimized for the most efficient implementation on the local platform.

**BN\_zero()**, **BN\_one()** and **BN\_set\_word()** set **a** to the values 0, 1 and **w** respectively.  **BN\_zero()** and **BN\_one()** are macros.

**BN\_value\_one()** returns a **BIGNUM** constant of value 1. This constant is useful for use in comparisons and assignment.

**BN\_get\_word()** returns **a**, if it can be represented as a **BN\_ULONG**.

## RETURN VALUES

**BN\_get\_word()** returns the value **a**, or all-bits-set if **a** cannot be represented as a single integer.

**BN\_one()** and **BN\_set\_word()** return 1 on success, 0 otherwise. **BN\_value\_one()** returns the constant. **BN\_zero()** never fails and returns no value.

## BUGS

If a **BIGNUM** is equal to the value of all-bits-set, it will collide with the error condition returned by **BN\_get\_word()** which uses that as an error value.

**BN\_ULONG** should probably be a typedef.

## SEE ALSO

**BN\_bn2bin**(3)

## HISTORY

In OpenSSL 0.9.8, **BN\_zero()** was changed to not return a value; previous versions returned an int.

## COPYRIGHT

Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use this file except in compliance with the License.  You can obtain a copy in the file LICENSE in the source distribution or at \<https://www.openssl.org/source/license.html\>.