BIO_f_prefix(3)

BIO_f_prefix(3) | OpenSSL | BIO_f_prefix(3)

# NAME

BIO_f_prefix, BIO_set_prefix, BIO_set_indent, BIO_get_indent - prefix BIO filter

# SYNOPSIS

     #include <openssl/bio.h>
     const BIO_METHOD *BIO_f_prefix(void);
     long BIO_set_prefix(BIO *b, const char *prefix);
     long BIO_set_indent(BIO *b, long indent);
     long BIO_get_indent(BIO *b);

# DESCRIPTION

BIO_f_cipher() returns the prefix BIO method. This is a filter for text output, where each line gets automatically prefixed and indented according to user input.

The prefix and the indentation are combined. For each line of output going through this filter, the prefix is output first, then the amount of additional spaces indicated by the indentation, and then the line itself.

By default, there is no prefix, and indentation is set to 0.

BIO_set_prefix() sets the prefix to be used for future lines of text, using prefix. prefix may be NULL, signifying that there should be no prefix. If prefix isn't NULL, this function makes a copy of it.

BIO_set_indent() sets the indentation to be used for future lines of text, using indent. Negative values are not allowed.

BIO_get_indent() gets the current indentation.

# NOTES

BIO_set_prefix(), BIO_set_indent() and BIO_get_indent() are implemented as macros.

# RETURN VALUES

BIO_f_prefix() returns the prefix BIO method.

BIO_set_prefix() returns 1 if the prefix was correctly set, or <=0 on failure.

BIO_set_indent() returns 1 if the prefix was correctly set, or <=0 on failure.

BIO_get_indent() returns the current indentation, or a negative value for failure.

# SEE ALSO

bio(7)

# COPYRIGHT

Copyright 2019 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>.

2026-06-09 | 3.5.7