用C反转字符串中的单词顺序（代码错误）

Question

Could someone guide me in the right direction with this ?

This is a school assignment which i just cant seem to find the error in. For the input

"a b c d e f" 

i get

"f e d c b a" and that is right.

But for

"1234567890 abcdefghij" i get 

"�' abcdefghij 1234567890"

Can someone guide me in the right direction? Are the pointers all wrong ?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{  
  char *words [100];
  char *word[11];
  char *str;
  int res, i;
  i = 0;
  res = scanf("%10s",word);
  if (res != 1) return 0;

  while ( res != EOF) {
    str = malloc(strlen(word)+1);
    strcpy(str,word);
    words[i] = str;
    res = scanf("%10s",word);
    i = i+1;
  }

  while (i>=0) {
    printf("%s ",words[i]);
    i--;
  }

  return 0;
}

Answer 1

i starts out 1 element past the end of the array. It's odd that the first example seems to work. Not surprising that the second does not.

Try:

while (--i >= 0)
{
  printf("%s ", words[i]);
}

and word should be char word[11] , not char *word[11] .

Answer 2

The problem is that i is one digit higher than the last filled index of your word so it is may potentially grab garbage.

instead of : i = i+1;

use:

if ( res != EOF) i = i+1;

Answer 3

why don't you use the strrev(str) function to reverse str ? i think that one is an easy way out

Answer 4

Your problem is int the print loop .

while (i>=0) {
    printf("%s ",words[i]);
    i--;
}

when you start this loop the value of i will give you an uninitialized element from the words array, change it this way

while (i > 0) {
    printf("%s ", words[--i]);
}

note : you should also free the pointers, so don't overwrite the words count, if it's only for ilustrative purpose, then it's ok, but even though you should do this

while (i > 0) {
    char *currentWord = words[--i];
    printf("%s ", currentWord);
    free(currentWord);
}

Answer 5

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*function splits a string into an array of words, returns the array and its actual dimension*/
/*------------------------------------------------------------------------------------------*/
char **StringToWords (char *buf, int &dim, int NW, int LW)
{
    char **words = (char**) malloc (NW*sizeof(char*));  
    int i = 0;
    for (; i<NW; i++)
        words[i] = (char*)malloc (LW*sizeof(char));     

    i = -1;
    char *delims = " ,.-";
    char *pch = strtok (buf, delims);
    while (pch != NULL && i<NW)
    {
        strcpy(words[++i], pch);
        pch = strtok (NULL, " ,.-");
    }
    dim = i+1;
    return words;
}

void DestroyWords (char **words, int NW)
{
    for (int i = 0; i<NW; i++)
        free (words[i]);
    free (words);
}

/*--------------------------------------------------------------------------------------------*/
int main()
{
    int NW = 100;   /*maximum number of words*/
    int LW = 50;    /*maximum length of a word*/

    char buf[BUFSIZ];
    printf("Your string:\n");
    gets(buf);

    int dim = 0;
    char **words = StringToWords (buf, dim, NW, LW);
    printf("Reversed string:\n");

    int i = dim;
    while (--i >-1)
        printf("%s ", words[i]);

    DestroyWords (words, NW);
    getchar();
    return 0;
}
/*--------------------------------------------------------------------------------------------*/