VIS(3) BSD Programmer's Manual VIS(3)
vis, strvis, strnvis, strvisx, svis, strsvis, strnsvis, strsvisx - visu- ally encode characters
#include <stdlib.h> #include <vis.h> char * vis(char *dst, int c, int flag, int nextc); int strvis(char *dst, const char *src, int flag); int strnvis(char *dst, const char *src, size_t size, int flag); int strvisx(char *dst, const char *src, size_t len, int flag); char * svis(char *dst, int c, int flag, int nextc, const char *extra); int strsvis(char *dst, const char *src, int flag, const char *extra); int strnsvis(char *dst, const char *src, size_t size, int flag, const char *extra); int strsvisx(char *dst, const char *src, size_t len, int flag, const char *extra);
The vis() function copies into dst a string which represents the charac- ter c. If c needs no encoding, it is copied in unaltered. The string is NUL 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 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 NUL. The flag parameter is used for altering the default range of characters considered for encoding and for altering the visual representation. The additional character, nextc, is only used when selecting the VIS_CSTYLE encoding format (explained below). The strvis(), strnvis() and strvisx() functions copy into dst a visual representation of the string src. The strvis() function encodes charac- ters from src up to the first NUL. The strnvis() function encodes charac- ters from src up to the first NUL or the end of dst, as indicated by size. The strvisx() function encodes exactly len characters from src (this is useful for encoding a block of data that may contain NULs). All three forms NUL terminate dst, except for strnvis() when size is zero, in which case dst is not touched. For strvis() and strvisx(), the size of dst must be four times the number of characters encoded from src (plus one for the NUL). strvis() and strvisx() return the number of characters in dst (not including the trailing NUL). strnvis() returns the length that dst would become if it were of unlimited size (similar to snprintf(3) or strlcpy(3)). This can be used to detect truncation but it also means that the return value of strnvis() must not be used without checking it against size. The functions svis(), strsvis(), strnsvis() and strsvisx() correspond to vis(), strvis(), strnvis(), and strvisx() but have an additional argument extra, pointing to a NUL terminated list of characters. These characters will be copied encoded or backslash-escaped into dst. These functions are useful e.g. to remove the special meaning of certain characters to shells. The encoding is a unique, invertible representation composed entirely of graphic characters; it can be decoded back into the original form using the unvis(3) or strunvis(3) functions. There are two parameters that can be controlled: the range of characters that are encoded (applies only to vis(), strvis(), strnvis(), and strvisx()), and the type of representation used. By default, all non- graphic characters except space, tab, and newline are encoded (see isgraph(3)). The following flags alter this: VIS_GLOB Also encode magic characters recognized by glob(3) ('*', '?', '[') and '#'. VIS_SP Also encode space. VIS_TAB Also encode tab. VIS_NL Also encode newline. VIS_WHITE Synonym for VIS_SP | VIS_TAB | VIS_NL. VIS_SAFE Only encode "unsafe" characters. These are control characters which may cause common terminals to perform unexpected func- tions. Currently this form allows space, tab, newline, back- space, bell, and return -- in addition to all graphic charac- ters -- unencoded. (The above flags have no effect for svis(), strsvis(), strnsvis(), and strsvisx(). When using these functions, place all graphic characters to be encoded in an array pointed to by extra. In general, the backslash character should be included in this array, see the warning on the use of the VIS_NOSLASH flag below). There are four forms of encoding. All forms use the backslash '\' charac- ter to introduce a special sequence; two backslashes are used to represent a real backslash, except VIS_HTTPSTYLE which uses '%'. These are the visual formats: (default) Use an 'M' to represent meta characters (characters with the 8th bit set), and use a caret '^' to represent control char- acters (see iscntrl(3)). The following formats are used: \^C Represents the control character 'C'. Spans characters '\000' through '\037', and '\177' (as '\^?'). \M-C Represents character 'C' with the 8th bit set. Spans characters '\241' through '\376'. \M^C Represents control character 'C' with the 8th bit set. Spans characters '\200' through '\237', and '\377' (as '\M^?'). \040 Represents ASCII space. \240 Represents Meta-space. VIS_CSTYLE Use C-style backslash sequences to represent standard non- printable characters. The following sequences are used to represent the indicated characters: \a - BEL (007) \b - BS (010) \f - NP (014) \n - NL (012) \r - CR (015) \s - (040) \v - VT (013) \0 - NUL (000) When using this format, the nextc parameter is looked at to determine if a NUL character can be encoded as '\0' instead of '\000'. If nextc is an octal digit, the latter representa- tion is used to avoid ambiguity. VIS_OCTAL Use a three digit octal sequence. The form is '\ddd' where d represents an octal digit. VIS_HTTPSTYLE Use URI encoding as described in RFC 1738. The form is '%xx' where x represents a hexadecimal digit. There is one additional flag, VIS_NOSLASH, which inhibits the doubling of backslashes and the backslash before the default format (that is, control characters are represented by '^C' and meta characters as 'M-C'). With this flag set, the encoding is ambiguous and non-invertible.
unvis(1), vis(1), snprintf(3), strlcpy(3), unvis(3) T. Berners-Lee, Uniform Resource Locators (URL), RFC1738.
The vis(), strvis() and strvisx() functions first appeared in 4.4BSD. The strnvis() function first appeared in OpenBSD 2.9. The svis(), strsvis(), and strsvisx() functions appeared in NetBSD 1.5. The strnsvis() function appeared in MirOS #10. MirOS BSD #10-current May 7, 2007 2
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