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Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" From: @(#)vis.3 8.1 (Berkeley) 6/9/93 .\" $FreeBSD: src/lib/libc/gen/vis.3,v 1.26 2004/07/17 12:27:25 tjr Exp $ .\" .Dd March 21, 2004 .Dt VIS 3 .Os .Sh NAME .Nm vis .Nd visually encode characters .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In vis.h .Ft char * .Fn vis "char *dst" "int c" "int flag" "int nextc" .Ft int .Fn strvis "char *dst" "const char *src" "int flag" .Ft int .Fn strvisx "char *dst" "const char *src" "size_t len" "int flag" .Sh DESCRIPTION The .Fn vis function copies into .Fa dst a string which represents the character .Fa c . If .Fa c needs no encoding, it is copied in unaltered. The string is null terminated, and a pointer to the end of the string is returned. The maximum length of any encoding is four characters (not including the trailing .Dv NUL ) ; thus, when encoding a set of characters into a buffer, the size of the buffer should be four times the number of characters encoded, plus one for the trailing .Dv NUL . The .Fa flag argument is used for altering the default range of characters considered for encoding and for altering the visual representation. The additional character, .Fa nextc , is only used when selecting the .Dv VIS_CSTYLE encoding format (explained below). .Pp The .Fn strvis and .Fn strvisx functions copy into .Fa dst a visual representation of the string .Fa src . The .Fn strvis function encodes characters from .Fa src up to the first .Dv NUL . The .Fn strvisx function encodes exactly .Fa len characters from .Fa src (this is useful for encoding a block of data that may contain .Dv NUL Ns 's ) . Both forms .Dv NUL terminate .Fa dst . The size of .Fa dst must be four times the number of characters encoded from .Fa src (plus one for the .Dv NUL ) . Both forms return the number of characters in dst (not including the trailing .Dv NUL ) . .Pp The encoding is a unique, invertible representation composed entirely of graphic characters; it can be decoded back into the original form using the .Xr unvis 3 or .Xr strunvis 3 functions. .Pp There are two parameters that can be controlled: the range of characters that are encoded, and the type of representation used. By default, all non-graphic characters except space, tab, and newline are encoded. (See .Xr isgraph 3 . ) The following flags alter this: .Bl -tag -width VIS_WHITEX .It Dv VIS_GLOB Also encode magic characters .Ql ( * , .Ql \&? , .Ql \&[ and .Ql # ) recognized by .Xr glob 3 . .It Dv VIS_SP Also encode space. .It Dv VIS_TAB Also encode tab. .It Dv VIS_NL Also encode newline. .It Dv VIS_WHITE Synonym for .Dv VIS_SP \&| .Dv VIS_TAB \&| .Dv VIS_NL . .It Dv VIS_SAFE Only encode "unsafe" characters. Unsafe means control characters which may cause common terminals to perform unexpected functions. Currently this form allows space, tab, newline, backspace, bell, and return - in addition to all graphic characters - unencoded. .El .Pp There are four forms of encoding. Most forms use the backslash character .Ql \e to introduce a special sequence; two backslashes are used to represent a real backslash. These are the visual formats: .Bl -tag -width VIS_HTTPSTYLE .It (default) Use an .Ql M to represent meta characters (characters with the 8th bit set), and use caret .Ql ^ to represent control characters see .Pf ( Xr iscntrl 3 ) . The following formats are used: .Bl -tag -width xxxxx .It Dv \e^C Represents the control character .Ql C . Spans characters .Ql \e000 through .Ql \e037 , and .Ql \e177 (as .Ql \e^? ) . .It Dv \eM-C Represents character .Ql C with the 8th bit set. Spans characters .Ql \e241 through .Ql \e376 . .It Dv \eM^C Represents control character .Ql C with the 8th bit set. Spans characters .Ql \e200 through .Ql \e237 , and .Ql \e377 (as .Ql \eM^? ) . .It Dv \e040 Represents .Tn ASCII space. .It Dv \e240 Represents Meta-space. .El .Pp .It Dv VIS_CSTYLE Use C-style backslash sequences to represent standard non-printable characters. The following sequences are used to represent the indicated characters: .Bd -unfilled -offset indent .Li \ea Tn - BEL No (007) .Li \eb Tn - BS No (010) .Li \ef Tn - NP No (014) .Li \en Tn - NL No (012) .Li \er Tn - CR No (015) .Li \et Tn - HT No (011) .Li \ev Tn - VT No (013) .Li \e0 Tn - NUL No (000) .Ed .Pp When using this format, the .Fa nextc argument is looked at to determine if a .Dv NUL character can be encoded as .Ql \e0 instead of .Ql \e000 . If .Fa nextc is an octal digit, the latter representation is used to avoid ambiguity. .It Dv VIS_HTTPSTYLE Use URI encoding as described in RFC 1808. The form is .Ql %dd where .Ar d represents a hexadecimal digit. .It Dv VIS_OCTAL Use a three digit octal sequence. The form is .Ql \eddd where .Ar d represents an octal digit. .El .Pp There is one additional flag, .Dv VIS_NOSLASH , which inhibits the doubling of backslashes and the backslash before the default format (that is, control characters are represented by .Ql ^C and meta characters as .Ql M-C ) . With this flag set, the encoding is ambiguous and non-invertible. .Sh SEE ALSO .Xr unvis 1 , .Xr unvis 3 .Rs .%A R. Fielding .%T Relative Uniform Resource Locators .%O RFC1808 .Re .Sh HISTORY These functions first appeared in .Bx 4.4 . .Sh BUGS The .Nm family of functions do not recognize multibyte characters, and thus may consider them to be non-printable when they are in fact printable (and vice versa.)