unvis(), strunvis()

decode visual representation of characters 

Function

SYNOPSIS

#include <vis.h>

int unvis(char *cp, int c, int *astate, int flag);

int strunvis(char *dst, const char *src);

DESCRIPTION

The unvis() and strunvis() functions are used to decode a visual representation of characters, as produced by the vis(), strvis() and strvisx() functions, back into the original form. The unvis() function is called with successive characters until a valid sequence is recognized, at which time the decoded character is available at the specified pointer. The strunvis() function decodes the characters at the specified source into the destination buffer.

The strunvis() function simply copies the source to the destination, decoding any escape sequences along the way, and returns the number of characters placed into the destination buffer, or -1 if an invalid escape sequence was detected. The size of the destination buffer should be equal to the size of the source buffer (that is, no expansion takes place during decoding).

The unvis() function implements a state machine that can be used to decode an arbitrary stream of bytes. All state associated with the bytes being decoded is stored outside the unvis() function (that is, a pointer to the state is passed in), so calls decoding different streams can be freely intermixed. To start decoding a stream of bytes, first initialize an integer to zero. Call unvis() with each successive, byte, along with a pointer to this integer, and a pointer to the destination character. The unvis() function has several return codes that must be handled properly. They are:

0  

Another character is necessary; nothing has been recognized yet.

UNVIS_VALID  

A valid character has been recognized and is available at the specified location.

UNVIS_VALIDPUSH  

A valid character has been recognized and is available at the specified location; however, the character currently passed in should be passed in again.

UNVIS_NOCHAR  

A valid sequence was detected, but no character was produced. This return code is necessary to indicate a logical break between characters.

UNVIS_SYNBAD  

An invalid escape sequence was detected, or the decoder is in an unknown state. The decoder is placed into the starting state.

When all bytes in the stream have been processed, call unvis() one more time with the flag set to UNVIS_END to extract any remaining character (the character passed in is ignored).

The following code fragment illustrates a proper use of unvis(): 

int state = 0;
char out;
while ((ch = getchar()) != EOF) {
	again:
	switch (unvis(&out, ch, &state, 0)) {
	case 0:
	case UNVIS_NOCHAR:
		break;
	case UNVIS_VALID:
		putchar(out);
		break;
	case UNVIS_VALIDPUSH:
		putchar(out);
		goto again;
	case UNVIS_SYNBAD:
		fprintf(stderr, "bad sequence!\n");
		exit(1);
	}
}
if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)
	putchar(out);

PARAMETERS

cp 

Pointer to stored character.

c 

Character to parse for conversion

astate 

Pointer to location in which state is stored

flag 

Should be 0 until the end of the input stream, at which time a final call should be made with flag set to UNVIS_END

dst 

Destination buffer for decoded characters.

src 

Buffer of characters to be converted.

RETURN VALUES

The unvis() function returns one of the state flags described above. The strunvis() function returns the number of characters stored to the destination buffer, or -1 on error.

CONFORMANCE

4.4BSD

MULTITHREAD SAFETY LEVEL

MT-Safe.

PORTING ISSUES

None.

AVAILABILITY

MKS Toolkit for Professional Developers
MKS Toolkit for Enterprise Developers
MKS Toolkit for Enterprise Developers 64-Bit Edition

SEE ALSO

Functions:
strvis(), strvisx(), vis()

MKS Toolkit 9.3 Documentation Build 6.