K&R C Bible Exercise 3-2

/*************************************************** /*Answer to Exercise 3-2, page 60 Write a function escape(s,t) that converts characters like newline and tab into visible escape sequences like /n and /t as it copies the string t to s . Use a switch . Write a function for the other direction as well, converting escape sequences into the real characters. ****************************************************/ #include <stdio.h> void escape(char * s, char * t); void unescape(char * s, char * t); int main(void) { char text1[50] = "/aHello,/n/tWorld! Mistakee/b was /"Extra 'e'/"!/n"; char text2[51]; printf("Original string:/n%s/n", text1); escape(text2, text1); printf("Escaped string:/n%s/n", text2); unescape(text1, text2); printf("Unescaped string:/n%s/n", text1); return 0; } /* Copies string t to string s, converting special characters into their appropriate escape sequences. The "complete set of escape sequences" found in K&R Chapter 2 is used, with the exception of: /? /' /ooo /xhh as these can be typed directly into the source code, (i.e. without using the escape sequences themselves) and translating them is therefore ambiguous. */ void escape(char * s, char * t) { int i, j; i = j = 0; while ( t[i] ) { /* Translate the special character, if we have one */ switch( t[i] ) { case '/n': s[j++] = '//'; s[j] = 'n'; break; case '/t': s[j++] = '//'; s[j] = 't'; break; case '/a': s[j++] = '//'; s[j] = 'a'; break; case '/b': s[j++] = '//'; s[j] = 'b'; break; case '/f': s[j++] = '//'; s[j] = 'f'; break; case '/r': s[j++] = '//'; s[j] = 'r'; break; case '/v': s[j++] = '//'; s[j] = 'v'; break; case '//': s[j++] = '//'; s[j] = '//'; break; case '/"': s[j++]= '//'; s[j] = '/"'; break; default: /* This is not a special character, so just copy it */ s[j] = t[i]; break; } ++i; ++j; } s[j] = t[i]; /* Don't forget the null character */ } /* Copies string t to string s, converting escape sequences into their appropriate special characters. See the comment for escape() for remarks regarding which escape sequences are translated. */ void unescape(char * s, char * t) { int i, j; i = j = 0; while ( t[i] ) { switch ( t[i] ) { case '//': /* We've found an escape sequence, so translate it */ switch( t[++i] ) { case 'n': s[j] = '/n'; break; case 't': s[j] = '/t'; break; case 'a': s[j] = '/a'; break; case 'b': s[j] = '/b'; break; case 'f': s[j] = '/f'; break; case 'r': s[j] = '/r'; break; case 'v': s[j] = '/v'; break; case '//': s[j] = '//'; break; case '/"': s[j] = '/"'; break; default: /* We don't translate this escape sequence, so just copy it verbatim */ s[j++] = '//'; s[j] = t[i]; } break; default: /* Not an escape sequence, so just copy the character */ s[j] = t[i]; } ++i; ++j; } s[j] = t[i]; /* Don't forget the null character */ }