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Question by Maverickmalai
Submitted on 8/25/2003
Related FAQ: comp.lang.c Answers to Frequently Asked Questions (FAQ List)
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My question
int x;

void test(char *)
{
  char *b, *c="heloworld";
  short z;
  z=0x41;
  b=(char *)malloc(sizeof(10));
  strcpy(b,"helloworld");
  printf("%d %d", b, &z);
  free(c);
}

1) where will the variable x will be stored?
   whether in stack, datasegement, heap.
2)where will be *c stored?
3)where will be helloworld stored?

4)while executing which line of the program the code get crashed?Reason






Answer by Suresh
Submitted on 10/29/2003
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Hi MaverickMalai,

1.  x will be stored in symbol table. All global variables will be stored in symbol table.

2.  All local variables will be stored in stack.

4. The command "free(c)" will crash or create segmentation violation. The following is the definition for "free " given by GNU.

"free() frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc(), calloc() or realloc()."

In your coding "c" is a char pointer whose value is assigned at the time of declaration. No memory is allocated explicitly using "malloc" or "realloc". Attempting to freeing a memory which is not created explicitly will crash the application.

 

Answer by z
Submitted on 2/5/2004
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You should malloc 10*sizeof(char), which allocates 10 spaces for char variables. Otherwise you have just malloc'd 10 bytes, which hardly is enough to store that largish string you have there.

 

Answer by viren
Submitted on 2/24/2004
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Hi there,

> 1) where will the variable x will be stored? whether in stack, datasegment, heap.

"x" will get stored in the BSS segment. A BSS segment is just like a Data segment - the differences being that BSS contains the un-initialised values and Data segment contains initialised values.

> 2)where will be *c stored?

The auto variable "c" would be stored on the stack. (as is the case with all other autos )

> 3)where will be helloworld stored?

The string "helloworld" is really a string literal (as is indicated to compiler by writing - char *c = "helloworld"; ) This string literal would be stored in the read-only Data segment. (Some compilers may give you the option to store it in the Code segment - e.g Code Warrior for PalmOS )

> 4)while executing which line of the program the code get crashed?Reason

free() call in C (or in C++) expects that the pointer that you are gonna pass on to free function, has some other useful info at the beginning of the memory pointed by that pointer. This is the reason why a free() call should always be given a pointer returned by malloc() (which writes the info needed by free() ). In your case, you are passing a pointer that lacks this info causing the system to go for toss. Hope this helps....if it does not, drop me a mail at drvirens@yahoo.com for more details.....

Cheers.

-Viren





 

Answer by Mahesh
Submitted on 11/18/2005
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All global and static variables will be stored in Data Segment (Again sub-divided into two, initialized and non - initialized DS).

String Literals will be stored in the Read Only segment. (U cannot edit such memory location).

And all the local defined/declared will be stored in Stack.

You can free memory, only if it is allocated using malloc/calloc !!!!!

 

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