[Dev-C++] Malloc Problem . Extra bytes !

[veenurs <ve...@ma...>]

Hi !
 It seems too simple .But what is it !?
 if( (buffer = ( PBYTE )calloc( 1000 ,sizeof(BYTE) )) == NULL ){
        ------
       -------
 }
   size = _msize( buffer );

 The size I get it is not 1000 , but 1008  ! Any subsequent call to 
realloc  does not add  the 8 bytes,though  .
[ Dev Cpp Version 4.9.7.0 ]
What's happening ?
BTW - "Generate debugging info" is OFF .
Thanks in advance .

-Rahul.

 
 

Luigi Santillo wrote:

> Iuri-
> Suppose that your problem is the following: you have a text file (say 
> it "script") with lines of different lengths, you wish to load a line 
> and print it on the screen until all the lines have been processed.
>
> script
> ------
> aaaaaa
> bbbbb
> iuri
> ------
>
> 1- assume that you know that no line has more than 10 chars
> Here is how I would solve it.
>
> #include <stdio.h>
> #include <assert.h>
>
> #define MAX_LEN 11
> #define FILE_NAME "script"
>
> int main()
> {
>    char buf[MAX_LEN];
>    FILE *inp = fopen(FILE_NAME, "r");
>
>    assert(inp != 0); /* a quick way to report errors */
>
>    while (fgets(buf, MAX_LEN, inp))
>       printf("%s", buf);
>
>    fclose(inp);
>
>    return 0;
> }
>
> As you can see the second argument of fgets is the size of the array 
> where the line will be stored, not the size of the line that will be 
> read. Also keep in mind that fgets will read only MAX_LEN - 1 = 10 
> chars, the last one will be used by fgets as the place for the '\0'.
> So when you write:
>
> fgets(linha1_ptr, sizeof(linha1_ptr), script);
>
> It is "strange" (because usually you already know how big a string 
> is), but OK, if by "sizeof(linha1_ptr)" you mean the length of the 
> string linha1_ptr before the call to fgets, it is not correct if you 
> mean: "read the line and get its length, return this length as the 
> value of sizeof(linha1_ptr)".
>
> Suppose you say: (assume linha1_ptr is an array of 31 chars)
>
> fgets(linha1_ptr, 31, script); /* and load the string "123\n" */
> /* now sizeof(linha1_ptr) is 4 */
>
> fgets(linha1_ptr, sizeof(linha1_ptr), script); /* trying to load 
> "iuri\n" */
> /* fgets will read 3 chars, "iur", the fourth will be '\0' */
>
>
> Of course when you say:
>
> fgets(linha1_ptr, 31, script); /* and load the string "123\n" */
> fgets(linha1_ptr, 31, script); /* trying to load "iuri\n" */
> /* now "iuri" will be loaded as expected */
>
> Hope this clearly explains what should be used as the second argument 
> of fgets.
>
> 2 - assume that you do not know the size of the biggest line
> Here is how I would solve it.
>
> #include <stdio.h>
> #include <assert.h>
> #include <string.h>
>
> #define FILE_NAME "script"
> char *getline(FILE *);
>
> int main(int argc, char *argv[])
> {
>    char *buf;
>    FILE *inp = fopen(FILE_NAME, "r");
>
>    assert(inp != 0);
>
>    while (buf = getline(inp))
>    {
>       printf("%s", buf);
>       free(buf);
>    }
>
>    fclose(inp);
>    return 0;
> }
>
> /*
> getline = read a line from the file, return the line read.
> The string that is returned is always terminated by a '\n'
> */
>
> #define SIZE 6
> #define GET_MEM (char *)calloc(len + 1, sizeof(char))
>
> char *getline(FILE *file)
> {
>    char buf[SIZE];
>    char *line = 0;
>    int len = 0;
>
>    while (fgets(buf, SIZE, file))
>    {
>       char *tmp = line;
>       int n = strlen(buf);
>
>       len += n;
>       line = GET_MEM;
>       assert(line != 0);
>
>       if (tmp)
>       {
>          strcpy(line, tmp);
>          free(tmp);
>       }
>
>       strcat(line, buf);
>
>       if (buf[n - 1] == '\n') /* finished reading line */
>          break;
>    }
>
>    return line;
> }
>
> Hope this is of some help
>
> At 14.46 18/07/01 -0300, you wrote:
>
>> Dear Luigi,
>>         Thank you for your help. I tried to use calloc because de 
>> string read from the
>> file string has diferent sizes. I.e. the first line of the file 
>> script is "iuri", when I write:
>> fgets (linha1_ptr ,sizeof(linha1_ptr), script);
>>         It returns: iur
>> If I write:
>> fgets (linha1_ptr , 30 , script);
>>         It returns: iuri
>>
>> With static memory the problem is that it reads the hole thing:
>> So if my string is:
>>         aaaaaaaaaa
>>         bbbb
>> With the fgets it will read:
>>         aaaaaaaaaa
>>         bbbb\0aaaa
>>
>> I think with sizeof it shouldn't happen, but it does. He reads the 
>> size of the 1º line and
>> returns this same size for every line, even if it's bigger.
>>
>>                                 Thanks,
>>                                                 Iuri
>
>
> ---
> gisan
>
>
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