Need help with simple XOR function

[Marton]

Hi, I need a bit of help with this function...
What I'm trying to do is call the function with a string, XOR it with value 255 and save it to the file. If I put a value of 0 to the XOR (leave as is) then it works properly, but if I put any value to XOR the original value with, then it doesn't work: it saves the previous XORed string constantly. Why could it be? I tried cleaning the "string" variable with "string = 0" and "string[0] = 0" but it does the same. Any clues?

Here is the code:

void write(char string[])
{
  int i;
  FILE *file;

  file=fopen("log.txt","ab+");

  if(file!=NULL)
  {
	  for(i=0;i<strlen(string);i++)
		string[i]^=255;
	  fputs(string,file);
  }


  fflush(file);
  fclose(file);

}

Many thanks in advance!

[dkalita]

give it a try with the following

string[i]^=(char)255;

[Marton]

Thanks! Today I woke up and had one of those flashes of "A-haaaa!" and fixed it. It turned out that for some reason (I'm still learning C), the string variable modifies the original variable (the one I was calling the function with) and I was using it later so the value was XORed and hence the problem. Here is the corrected function:

void write(char string[])
{
  int i;
  FILE *file;

  file=fopen("log.txt","ab+");

  if(file!=NULL)
  {
	  for(i=0;i<strlen(string);i++)
		string[i]^=0xff;
	  fputs(string,file);
	  for(i=0;i<strlen(string);i++)
		string[i]^=0xff;
  }


  fflush(file);
  fclose(file);

}

[dkalita]

U can do the same as follows:

void write(char string[])
{
  int i;
  FILE *file;
  char *strTemp=(char *)malloc(strlen(string)+1);
  strcpy(strTemp, string);

  file=fopen("log.txt","ab+");

  if(file!=NULL)
  {
	  for(i=0;i<strlen(string);i++)
		strTemp[i]^=0xff;
	  fputs(strTemp,file);
                  free(strTemp);
  }

  fflush(file);
  fclose(file);
}

This way u will save the number of operations done to the string.

[SVR]

Also it would be a good idea to save strlen(string) and instead of doing strlen in the for loop.

int iLen = strlen(string);

for(i = 0; i < iLen; i++)
...

Not only to save operations, but in the non- tempString version you could actually get the wrong length from the modified string.

[Marton]

Many thanks for the suggestions, guys! That'd help me for sure! Really appreciated.

[Aia]

U can do the same as follows:

void write(char string[])
{
  int i;
  FILE *file;
  char *strTemp=(char *)malloc(strlen(string)+1);
/*
 * Where would be that pointer be pointing to if malloc is not successful
* allocating memory? You must always check for the return of malloc.
* casting malloc is not necessary if you include the proper stdlib.h header file
*/
  strcpy(strTemp, string); /* might be writing where there's no memory available, creating segmentation fault */

  file=fopen("log.txt","ab+");
/* 
 * You check if the file was opened successfully, but you do not provide
 * a solution if the file couldn't be opened properly
*/

  if(file!=NULL)
  {
	  for(i=0;i<strlen(string);i++)
		strTemp[i]^=0xff;
	  fputs(strTemp,file);
                  free(strTemp); /* If the file was not opened, you never released the memory allocated before going into the if statement, creating a memory leak */
  }

  fflush(file);
  fclose(file); /* you might be closing a file that it was never opened */
}

This way u will save the number of operations done to the string.

It is best if code is as proper as possible when posting to show how's done.

[dkalita]

It is best if code is as proper as possible when posting to show how's done.

thanks for that suggestion. I will keep those in mind.