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163 lines
4.0 KiB
C
163 lines
4.0 KiB
C
/*
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* File: scanadt.c
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* ---------------
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* This file implements the scanadt.h interface.
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*/
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#include <stdio.h>
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#include <ctype.h>
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#include "genlib.h"
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#include "strlib.h"
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#include "scanadt.h"
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/*
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* Type: scannerCDT
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* ----------------
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* This structure is the concrete representation of the type
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* scannerADT, which is exported by this interface. Its purpose
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* is to maintain the state of the scanner between calls. The
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* details of the representation are invisible to the client,
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* but consist of the following fields:
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*
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* str -- Copy of string passed to SetScannerString
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* len -- Length of string, saved for efficiency
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* cp -- Current character position in the string
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* savedToken -- String saved by SaveToken (NULL indicates none)
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* spaceOption -- Setting of the space option extension
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*/
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struct scannerCDT {
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string str;
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int len;
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int cp;
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string savedToken;
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spaceOptionT spaceOption;
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};
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/* Private function prototypes */
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static void SkipSpaces(scannerADT scanner);
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static int ScanToEndOfIdentifier(scannerADT scanner);
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/* Exported entries */
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scannerADT NewScanner(void)
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{
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scannerADT scanner;
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scanner = New(scannerADT);
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scanner->str = NULL;
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scanner->spaceOption = PreserveSpaces;
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return (scanner);
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}
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void FreeScanner(scannerADT scanner)
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{
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if (scanner->str != NULL) FreeBlock(scanner->str);
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FreeBlock(scanner);
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}
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void SetScannerString(scannerADT scanner, string str)
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{
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if (scanner->str != NULL) FreeBlock(scanner->str);
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scanner->str = CopyString(str);
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scanner->len = StringLength(str);
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scanner->cp = 0;
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scanner->savedToken = NULL;
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}
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string ReadToken(scannerADT scanner)
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{
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char ch;
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string token;
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int start, finish;
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if (scanner->str == NULL) {
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Error("SetScannerString has not been called");
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}
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if (scanner->savedToken != NULL) {
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token = scanner->savedToken;
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scanner->savedToken = NULL;
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return (token);
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}
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if (scanner->spaceOption == IgnoreSpaces) SkipSpaces(scanner);
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start = finish = scanner->cp;
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if (start >= scanner->len) return (CopyString(""));
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ch = scanner->str[scanner->cp];
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if (isalnum(ch)) {
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finish = ScanToEndOfIdentifier(scanner);
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} else {
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scanner->cp++;
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}
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return (SubString(scanner->str, start, finish));
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}
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bool MoreTokensExist(scannerADT scanner)
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{
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if (scanner->str == NULL) {
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Error("SetScannerString has not been called");
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}
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if (scanner->savedToken != NULL) {
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return (!StringEqual(scanner->savedToken, ""));
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}
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if (scanner->spaceOption == IgnoreSpaces) SkipSpaces(scanner);
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return (scanner->cp < scanner->len);
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}
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void SaveToken(scannerADT scanner, string token)
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{
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if (scanner->str == NULL) {
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Error("SetScannerString has not been called");
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}
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if (scanner->savedToken != NULL) {
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Error("Token has already been saved");
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}
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scanner->savedToken = token;
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}
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void SetScannerSpaceOption(scannerADT scanner, spaceOptionT option)
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{
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scanner->spaceOption = option;
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}
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spaceOptionT GetScannerSpaceOption(scannerADT scanner)
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{
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return (scanner->spaceOption);
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}
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/* Private functions */
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/*
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* Function: SkipSpaces
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* Usage: SkipSpaces(scanner);
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* ---------------------------
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* This function advances the position of the scanner until the
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* current character is not a whitespace character.
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*/
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static void SkipSpaces(scannerADT scanner)
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{
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while (isspace(scanner->str[scanner->cp])) {
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scanner->cp++;
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}
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}
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/*
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* Function: ScanToEndOfIdentifier
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* Usage: finish = ScanToEndOfIdentifier(scanner);
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* -----------------------------------------------
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* This function advances the position of the scanner until it
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* reaches the end of a sequence of letters or digits that make
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* up an identifier. The return value is the index of the last
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* character in the identifier; the value of the stored index
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* cp is the first character after that.
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*/
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static int ScanToEndOfIdentifier(scannerADT scanner)
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{
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while (isalnum(scanner->str[scanner->cp])) {
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scanner->cp++;
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}
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return (scanner->cp - 1);
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}
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