Reversing file input

[Passwaters]

I can get the code to flip every string/word. But i need to stop strings when they include special characters.
INPUT: Homework 1 is due on Friday. Good$$?Luck!
OUTPUT: krowemoH 1 si eud no .yadirF !kcuL?$$dooG
The output should be krowemoH 1 si eud no yadirF. dooG$$?kcuL!.

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

void reverse_string(char*);
void reverse_words(char*);

int main()
{

FILE *fp;
char Input[255];
fp = fopen("test.txt", "r");
fgets(Input, 255, (FILE*)fp);
printf("%s\n", Input);
reverse_words(Input);
printf("\n%s", Input);

  return 0;
}

void reverse_words(char *s) {
  char b[100], *t, *z;
  int c = 0;

  t = s;

  while(*t) {                           //processing complete string
    while(*t != ' ' && *t != '\0') {    //extracting word from string
      b[c] = *t;
      t++;
      c++;
    }
    b[c] = '\0';
    c = 0;

    reverse_string(b);        // reverse the extracted word

    z = b;

    while (*z) {    //copying the reversed word into original string
      *s = *z;
      z++;
      s++;
    }

    if (*s == ' ') //Skipping spaces
        {
            s++;
        }
    t = s;                              // pointing to next word
  }


}


void reverse_string(char *t) {
  int l, c;
  char *e, s, *z;
  l = strlen(t);
  e = t + l - 1;
  z = t + l - 2;

  for (c = 0; c < l/2; c++) {
    s  = *t;
    *t = *e;
    *e = s;
    t++;
    e--;
    }
}

[laserlight]

This is not a good idea:

void reverse_words(char *s) {
  char b[100], *t, *z;
  int c = 0;

What I mean is that you declared five variables, all of which having single character names. Such variable names are common for loop and array indices, perhaps for variables in a very small scope such that their purpose and meaning is blatantly obvious, and sometimes for certain domain-specific purposes, but otherwise they tend to be poorly chosen because they are not descriptive.

Since you seem to be willing to work with pointers, I suggest an entirely in-place version of what you are trying to do, inspired by the loop structure that you outlined:

void reverse_words(char *text) {
    char *word_start = text;
    char *word_end;
    while (*word_start != '\0') {
        /* use a loop to increment word_start until it points to a character
           that is a '\0', or is neither whitespace nor a special character
           ... */

        word_end = word_start;
        /* use a loop to increment word_end until it points to a character that
           is a '\0', whitespace, or a special character
           ... */

        reverse_word(word_start, word_end);
        word_start = word_end;
    }
}

void reverse_word(char *word_start, char *word_end) {
    /* reverse the word using the start and end pointers, keeping in mind that
       word_end points to the character immediately after the word's last
       non-special character, so you should not alter what it points to;
       one way to do this is to first decrement word_end, then loop to
       increment word_start and decrement word_end until word_start is no
       longer less than word_end, swapping characters as you go
       ... */
}

[Kernelpanic]

Reverse a string is a shortly programm only. For Your special whishes You have to a little bit experiment.
Compiled with GCC for Windows.

//Reverse a string, 24. Sept. 2018

#include<stdio.h>
#include<string.h>
 
int main(void)
{
   char zeichenkette[100];
  
  printf("Give me a string: ");
  gets(zeichenkette);
    
   printf("Zeichenkette orginal: %s\n\n",zeichenkette); 
  
  // -strrev- reverse a string
  //-strdup- calls malloc() for check of space
   printf("Zeichenkette after rerverse: %s",strrev(strdup(zeichenkette)));
 
   return 0;
}

[rstanley]

Reverse a string is a shortly programm only. For Your special whishes You have to a little bit experiment.
Compiled with GCC for Windows.

//Reverse a string, 24. Sept. 2018

#include<stdio.h>
#include<string.h>
 
int main(void)
{
   char zeichenkette[100];
  
  printf("Give me a string: ");
  gets(zeichenkette);
    
   printf("Zeichenkette orginal: %s\n\n",zeichenkette); 
  
  // -strrev- reverse a string
  //-strdup- calls malloc() for check of space
   printf("Zeichenkette after rerverse: %s",strrev(strdup(zeichenkette)));
 
   return 0;
}

strrev() is not a Standard Library function. It is not available on Linux.

gets() is depreciated under C99, and has been removed as of C11. Please use fgets() instead!

If you use strdup(), you should free() the pointer returned from the function, even if it is near the end of the program.

[Kernelpanic]

Yes, gets() is outdated says MS. But the newest GCC (mingw) compiled it without mistake message. It use maybe the MS Library. - fgets() coming later.

//Reverse a string, 24. Sept. 2018
//For Window-Systems only - strrev, strdup


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


int main(void)
{
   char zeichenkette[100];
   char *zgr = zeichenkette;
     
   printf("Give me a string: ");
   gets(zeichenkette);
          
   printf("\n");
   printf("Zeichenkette original: %s\n\n",zgr); 
     
   // -strrev- reverse a string
   //-strdup- calls malloc() for check of space
   printf("Zeichenkette after reverse: %s",strrev(strdup(zgr)));
   free(zgr);
 
   return 0;

[jimblumberg]

Yes, gets() is outdated says MS. But the newest GCC (mingw) compiled it without mistake message.

Then you're compiler is probably not properly set up.

Here is what my compiler says about your program:

||=== Build: Debug in chomework (compiler: GCC 8-1) ===|
main.c||In function ‘main’:|
main.c|16|error: implicit declaration of function ‘gets’; did you mean ‘fgets’? [-Wimplicit-function-declaration]|
main.c|23|error: implicit declaration of function ‘strrev’; did you mean ‘strlen’? [-Wimplicit-function-declaration]|
main.c|23|error: implicit declaration of function ‘strdup’; did you mean ‘strcmp’? [-Wimplicit-function-declaration]|
main.c|23|warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘int’ [-Wformat=]|
||=== Build failed: 3 error(s), 1 warning(s) (0 minute(s), 0 second(s)) ===|

Using the current C standard the gets() function is no longer depreciated, it has actually been removed from the standard. The strrev() and strdup() functions are not standard C functions not available on my system.

[Kernelpanic]

So, now it's enough! Last post was too early!
Compiled like before - no mistakes.

//Reverse a string, 25. Sept. 2018
//Benutzt fgets()
//For Window-Systems only - strrev, strdup


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


#define MAX 100


int main(void)
{
   char zeichenkette[MAX];
   char *zgr = zeichenkette;
     
   printf("Give me a string: ");
   fgets(zeichenkette, MAX, stdin);
          
   printf("\n");
   printf("Zeichenkette original: %s\n\n",zgr); 
     
     // -strrev- reverse a string
    //-strdup- calls malloc() for check of space
   printf("Zeichenkette after reverse: %s",strrev(strdup(zgr)));
   free(zgr);
 
   return 0;
}

[jimblumberg]

Where did you manually allocate (with malloc/calloc) the memory that you're freeing on line 28?

Why do you even need that pointer?

[rstanley]

strdup() duplicates the string passed by malloc'ing the data space, that free() needs to be called to free up the memory.

Actually, "zgr" is not the pointer that should be freed!!!

The pointer returned from strdup() should be captured to a pointer, then THAT pointer should be freed after!!! That address is being used by printf() but then thrown away!!! I didn't catch that! ;^)

[Kernelpanic]

Where did you manually allocate (with malloc/calloc) the memory that you're freeing on line 28?

Why do you even need that pointer?

This is because strdup () calls malloc () to check if there is enough space for the operation. And this area should given free after operation.


With the pointer the program is working - no mistake messages from the gcc.

[Kernelpanic]

strdup() duplicates the string passed by malloc'ing the data space, that free() needs to be called to free up the memory.

Actually, "zgr" is not the pointer that should be freed!!!

The pointer returned from strdup() should be captured to a pointer, then THAT pointer should be freed after!!! That address is being used by printf() but then thrown away!!! I didn't catch that! ;^)

Now it gets complicated! I will see it tomorrow ...

[laserlight]

Now it gets complicated! I will see it tomorrow ...

I suggest that you start your own thread. Although Passwaters has not replied in more than 3 days, you're still derailing Passwaters' post with your own as your solution has nothing to do with Passwaters' problem other than the word "reverse": you're reversing entire strings, whereas Passwaters wants to effectively tokenise a string (read from file) to reverse "word" by "word" with consideration for certain special characters.