Manipulating strings in C

Slougi · Mar 23, 2003

aprentice said:
Stop confusing slougi with jibberish examples of your "l33t skills" First of all, pointers point at the address of the array holding the data. There, was that too hard to explain?

Yes pointers point to a mem address. I still don't see why they cannot hold any arbitrary data, and for all intends and purposes, they should be able to.

aprentice · Mar 23, 2003

Slougi said:
Yes pointers point to a mem address. I still don't see why they cannot hold any arbitrary data, and for all intends and purposes, they should be able to.

Because the point of pointers is the point?

Slougi · Mar 23, 2003

aprentice said:
Because the point of pointers is the point?

Code:

#include < stdio.h >
                                                                                                                
int main()
{
   FILE *xmms;
   char *song;
   if ((xmms = fopen("/home/louai/.xmms_song" , "r")) == NULL)
     {
        printf("Failed while loading file!\n");
        return 1;
     }
   printf("File is read!\n");
   song=(char *) malloc(sizeof(xmms));
   while (fgets(song, 200, xmms) != NULL)
     {
        printf("%s", song);
     }
   free(song);
   return 0;
}

Is anything wrong here? Again, excuse extra spaces that are due to HTML.

Slougi · Mar 23, 2003

Oh, and how would I read a file from a users home directory? Would I need to use environment variables?

Code:

fopen("~/file", "r");

Does not work.

Slougi · Mar 23, 2003

Also why does fclose(xmms); cause a crash?!

aprentice · Mar 23, 2003

Slougi said:
Oh, and how would I read a file from a users home directory? Would I need to use environment variables?

Code:

fopen("~/file", "r");

Does not work.

Are you coding in windows or linux?

aprentice · Mar 23, 2003

Slougi said:
Also why does fclose(xmms); cause a crash?!

Maybe the file was never opened to begin with if there was an error.

GuestX · Mar 23, 2003

aprentice said:
Are you coding in windows or linux?

Slougi said:
As to DOS limitations, no worry, I use Linux

I think Linux :happy:

Slougi · Mar 23, 2003

aprentice said:
Maybe the file was never opened to begin with if there was an error.

Nope it was. Look at the code above.

Slougi · Mar 23, 2003

aprentice said:
Are you coding in windows or linux?

Linux. Haven't touched windows in erm 2 months?

euphoria · Mar 24, 2003

Slougi said:

Code:

#include < stdio.h > int main() { FILE *xmms; char *song; if ((xmms = fopen("/home/louai/.xmms_song" , "r")) == NULL) { printf("Failed while loading file!\n"); return 1; } printf("File is read!\n"); song=(char *) malloc(sizeof(xmms)); while (fgets(song, 200, xmms) != NULL) { printf("%s", song); } free(song); return 0; }

Is anything wrong here? Again, excuse extra spaces that are due to HTML.

song=(char *) malloc(sizeof(xmms)); // <-- BAD!
xmms is type (FILE *) is only pointer to the file handle and its size is 4 bytes (32-bit pointer) and its not the size of the file. One way to do it is like this:

Code:

BOOL W32LoadROM(ROM_T *rom)
{
	rom->file_handle = fopen(rom->filename, "rb");
	if (!rom->file_handle)
	{
		log_error("Couldn't open %s", rom->filename);
		return FALSE;
	}
	else
	{
		size_t ret;
		struct stat sbuf;

		fstat(fileno(rom->file_handle), &sbuf);
		rom->filesize = sbuf.st_size;
		rom->filebuffer = (u8 *)malloc(rom->filesize);
		ret = fread(rom->filebuffer, 1, rom->filesize, rom->file_handle);
		fclose(rom->file_handle);
		if (ret != rom->filesize)
		{
			log_error("fread() returned wrong size!");
			return FALSE;
		}
	}
	return TRUE;
}

euphoria · Mar 24, 2003

Code:

getenv
Syntax

#include <stdlib.h>
char *getenv(const char *name);
Description
Get the setting of the environment variable name. Do not alter or free the returned value. 
Return Value
The value, or NULL if that variable does not exist. 
Portability
ANSI, POSIX 
Example

char *term = getenv("TERM");

Here's getenv() from libc-2.02 manual hope it helps

Slougi · Mar 24, 2003

euphoria said:
song=(char *) malloc(sizeof(xmms)); // <-- BAD!
xmms is type (FILE *) is only pointer to the file handle and its size is 4 bytes (32-bit pointer) and its not the size of the file. One way to do it is like this:

Code:

BOOL W32LoadROM(ROM_T *rom) { rom->file_handle = fopen(rom->filename, "rb"); if (!rom->file_handle) { log_error("Couldn't open %s", rom->filename); return FALSE; } else { size_t ret; struct stat sbuf; fstat(fileno(rom->file_handle), &sbuf); rom->filesize = sbuf.st_size; rom->filebuffer = (u8 *)malloc(rom->filesize); ret = fread(rom->filebuffer, 1, rom->filesize, rom->file_handle); fclose(rom->file_handle); if (ret != rom->filesize) { log_error("fread() returned wrong size!"); return FALSE; } } return TRUE; }

Woooh :crazy:
Wanna explain what is going on?

Slougi · Mar 24, 2003

Another go. Is this any good? Seems to work 100% now.

Code:

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

int main()
{
   FILE *xmms;
   char *song;
   int filesize;
   if ((xmms = fopen("/home/all/slougi/.xmms_song" , "r")) == NULL)
     {
        printf("Failed while loading file!\n");
        return 1;
     }
   printf("File is read!\n");
   fseek(xmms,0,SEEK_END);
   filesize=ftell(xmms);
   rewind(xmms);
   song=(char *) malloc(filesize);
   while (fgets(song, 200, xmms) != NULL)
     {
        printf("%s", song);
     }
   fclose(xmms);
   free(song);
   return 0;
}

I am not sure whether I need to include stdlib, but was told to do it so there

Doomulation · Mar 24, 2003

Well, I don't see any errors in it!

Although I prefer new and delete

Slougi · Mar 24, 2003

Doomulation said:
Well, I don't see any errors in it!
Although I prefer new and delete

I'll take a look at em

This was just the simplest solution that I found.

euphoria · Mar 24, 2003

Slougi said:
Woooh :crazy:
Wanna explain what is going on?

Code:

BOOL W32LoadROM(ROM_T *rom)
{
  rom->file_handle = fopen(rom->filename, "rb");
  if (!rom->file_handle)
  {
    log_error("Couldn't open %s", rom->filename);
    return FALSE;
  }

// Above opens file and if it fails prints a error message. log_error(const char *, ...) is m own function. ignore it.

  else
  {
    size_t ret; // size_t is unsigned int
    struct stat sbuf; // struct stat is what fstat needs
    fstat(fileno(rom->file_handle), &sbuf); // get file statistics of file rom->file_handle
    rom->filesize = sbuf.st_size; // get file's size and puts it to rom->filesize
    rom->filebuffer = (u8 *)malloc(rom->filesize); // allocates memory for filebuffer
    ret = fread(rom->filebuffer, 1, rom->filesize,  rom->file_handle); // reads rom->filesize amount of bytes from rom->file_handle and puts them in rom->filebuffer
    fclose(rom->file_handle); // closes rom->file_handle ;)
    if (ret != rom->filesize) // if ret (amoun of bytes read by fread) is different from rom->filesize it prints an error message 
    {
      log_error("fread() returned wrong size!");
      return FALSE;
    }
  }
  return TRUE;
}

hope this helps a bit. i don't know how much you know about c but rom is a pointer to a structure which has elements that are accessed with '->' operator.

like:
typedef struct {
int value1;
char *pointer1;
} kakka;

and then you declare it
kakka *k;

allocate mem for it:
k = (kakka *)malloc(sizeof(kakka));

access it:
kakka->value1 = 1;
kakka->pointer1 = pointer_to_some_string_for_example;

and free it at the end:
free(kakka);

Slougi · Mar 24, 2003

Ok that makes it a lot clearer, thanks

And as you can see, my C knowldge is very limited

IIRC "x->y" is the same as "(*x).y", is that correct?

icepir8 · Mar 24, 2003

yes.

Alot easier to type and few misstakes are likely to be made. Easier to read too.

Doomulation · Mar 25, 2003

euphoria said:
hope this helps a bit. i don't know how much you know about c but rom is a pointer to a structure which has elements that are accessed with '->' operator.

like:
typedef struct {
int value1;
char *pointer1;
} kakka;

and then you declare it
kakka *k;

allocate mem for it:
k = (kakka *)malloc(sizeof(kakka));

access it:
kakka->value1 = 1;
kakka->pointer1 = pointer_to_some_string_for_example;

and free it at the end:
free(kakka);

I find it just easier to use new/delete.

Code:

typedef struct {
  int value1;
  char *pointer1;
} kakka;

int main()
{
  kakka* k = new kakka;
  or...
  kakka* k = new kakka[arrays];

  delete k;
  or...
  delete [] k;
}

I think it's possible in c. It should be

it works at least with vc++.
Anyway, when using delete, use the seconds statement to delete arrays of the pointer. Otherwise youuse the first statement.

Manipulating strings in C

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