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Re^2: Five Ways to Reverse a String of Words (ANSI C version)

by salva (Canon)
on Mar 06, 2015 at 12:28 UTC ( #1119021=note: print w/replies, xml ) Need Help??


in reply to Re: Five Ways to Reverse a String of Words (ANSI C version)
in thread Five Ways to Reverse a String of Words (C#, Perl 5, Perl 6, Ruby, Haskell)

A reverse-words-in-place C version:
#include <stdio.h> #include <stdlib.h> char * readlinef(FILE *stream) { int buffer_len = 0; int len = 0; char *buffer; while (1) { int c = fgetc(stream); switch (c) { case '\n': if (!len) continue; case EOF: if (buffer) buffer[len] = '\0'; return buffer; default: if (len >= buffer_len) { buffer_len = buffer_len * 2 + 100; buffer = (char *)realloc(buffer, buffer_len + 1); } buffer[len++] = c; } } } void reverse(char *start, char *end) { while (start < --end) { char tmp = *end; *end = *start; *(start++) = tmp; } } char * skip_spaces(char *p) { while (isspace(*p)) p++; return p; } char * skip_word(char *p) { while (*p && !isspace(*p)) p++; return p; } int main(int argc, char *argv[]) { char *line; while (line = readlinef(stdin)) { char *start = line; while (1) { char *word_start = skip_spaces(start); char *word_end = skip_word(word_start); if (word_start == word_end) { if (start != line) start--; break; } reverse(start, word_end); start += word_end - word_start; if (*start == '\0') break; start++; } reverse(line, start); *start = '\0'; fprintf(stdout, "%s\n", line); free(line); } }

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Re^3: Five Ways to Reverse a String of Words (ANSI C version)
by BrowserUk (Pope) on Mar 06, 2015 at 15:25 UTC

    My try inspired by bitingduck's triple reverse:

    #include <stdio.h> #include <string.h> void reverse( char*p, int n ) { char c, *e = p+n-1; n /= 2; while( n-- ) c = *p, *p++ = *e, *e-- = c; } char *reverseWords( char*line ) { int len = (int)strlen( line ); char *p = line, *p1 = line, *e = line+len; reverse( line, len ); while( p <= e ) { if( *p == 32 || *p == 0 ) { reverse( p1, (int)( p - p1) ); p1 = p+1; } ++p; } return line; } int main( int argc, char **argv ) { char line[ 1024 ]; printf( "%s\n", reverseWords( gets_s( line, 1024 ) ) ); return 0; }

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