反向字符数组中的单词

Question

for exemple i need to invers "Paris" to "siraP"...

My main:

int main(void)
{
    char w1[] = "Paris";
    ReverseWord(w1);
    printf("The new word is: %s",w1);
    return0;
}

and my function:

void ReverseWord(char *Str)
{
     int counter=0;
     for(int i=0; *(Str+i)!='\0'; i++)
          counter++;

     int length = counter-1;

     char temp[length];

     for(int j=0; temp[j]=='\0'; j++)
          temp[j]=Str[length-j];
}

Now I have my renverse word in temp[]. I need to put it in my pointer *Str. How can I do it??

Thanks

Answer 1

If you want use temp must then your function like this

void ReverseWord(char *Str)
{
    int i,j;

    if(str)
    {
      int length=strlen(Str);
      char temp[length+1];

      for( j=0; j<length; j++)
          temp[j]=Str[length-1-j];

      temp[j]='\0';

      strcpy(Str,temp);
   }

}

Without using temp as follows

void ReverseWord(char *Str)
{
    int end= strlen(Str)-1;
    int start = 0;

    while( start<end )
    {
        Str[start] ^= Str[end];
        Str[end] ^= Str[start];
        Str[start]^= Str[end];

        ++start;
        --end;
    }
}

Answer 2

void ReverseWord(char *Str)
{
    size_t len;
    char temp, *end;

    len = strlen(Str);
    if (len < 2)
        return;

    end = Str + len - 1;
    while (end > Str)
    {
        temp = *end;
        *end-- = *Str;
        *Str++ = temp;
    }
}

Answer 3

One more option, this time with dangerous malloc(3).

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

char *rev(char s[]) {
  char *buf = (char *)malloc(sizeof(char) * strlen(s));
  int i, j;

  if(buf != NULL)
    for(i = 0, j = strlen(s) - 1; j >= 0; i++, j--)
      buf[i] = s[j];

  return buf;
}

int main(int argc, char **argv) {
  printf("%s\n", rev(argv[1]));
  return 0;
}

Run with "foo bar foobar baz" and get zab raboof rab oof back:

~/tmp$ ./a.out "foo bar foobar baz"
zab raboof rab oof

Answer 4

Here I think you can study two algorithms:

1. C string length calculate: the end of the c string is '\\0'
2. How to reverse ac string in place

And if you need to test the code, you should alloc testing strings in heap or strack. If you write a literal string, you may meet a bus error because of the literal string being saved in text-area which is a read only memory.

And the following is the demo:

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

void reverse_string(char* str)
{
    size_t len;
    char tmp, *s;
    //Get the length of string, in C the last char of one string is \0
    for(s=str;*s;++s) ;
    len = s - str;

    //Here we use the algorithm for reverse the char inplace.
    //We only need a char tmp place for swap each char
    s = str + len - 1;
    while(s>str){
        tmp = *s;
        *s = *str;
        *str = tmp;
        s--;
        str++;
    }
}

int main()
{
    char* a = "abcd";
    //Here "abcd" will be saved in READ Only Memory. If you test code, you will get a bus error.
    char* b = (char*)calloc(1,10);
    strcpy(b,a);
    reverse_string(b);
    printf("%s\n",b);

    a = "abcde";
    strcpy(b,a);
    reverse_string(b);
    printf("%s\n",b);
}

Answer 5

you can do it simply by following code

for(int k=0;k<strlen(temp);k++)
     {
        Str[k]=temp[k];
     }