CODEWITHSUNDEEP
c
jcrshankar
jcrshankar

Reputation: 83

error in double value

char *format_double_trans_amount(double amount)

{

   char amount_array_n[25];

   strcpy(amount_array_n,""); 

   printf("\nInitial  value ***** %s",amount_array_n);

   printf("\nDouble amount ***** %f",amount);

   sprintf(amount_array_n,"%1f",amount);

   printf("\nFinal ........ %s",  amount_array_n);

   printf("\nReturn ---- %s",amount_array_n);

   return amount_array_n;
}

int main()
{

printf ("\nformat_format_double_trans_amount: %s ************", format_double_trans_amount(1000.123400));

}

the result in the main method gives dump value could anybody please help me on this? output:

Initial value *

Double amount * 1000.123400

Final ........ 1000.123400

Return ---- 1000.123400

format_format_double_trans_amount: /ò# ($$Ð/Òð

Upvotes: 0

Views: 105

Answers (5)

Julio Gorgé
Julio Gorgé

Reputation: 10106

You are returning a pointer to amount_array_n at end of the function format_double_trans_amount(), however the scope of that stack allocated array is limited to the body of the function. Trying to access that memory area after exiting the function will result in undefined behaviour (at best rubbish displayed and at worst a crash).

The quick and dirty fix to your program is adding static to amount_array_n:

static char amount_array_n[25];

That would make the array an effective global variable. Still, not a very elegant solution, just a quick fix for your test program.

Upvotes: 1

atoMerz
atoMerz

Reputation: 7672

amount_array_n is local variable, when you return its pointer to main function, it won't have a valid address that's why you get that output.

Upvotes: 0

Prasoon Saurav
Prasoon Saurav

Reputation: 92854

amount_array_n being local to the function gets destroyed after the function returns. Using the returned value would invoke Undefined Behaviour.

Upvotes: 2

Chris Lutz
Chris Lutz

Reputation: 75389

When your function returns, the character array it allocated is deallocated, so when you return a pointer to that array, the pointer becomes invalid. Returning it is undefined behavior, which means the compiler can do anything. If you're really unlucky, it'll work, and you won't realize you have a problem until years later when your whole program breaks and you have no idea why. In most cases, you get garbage values or crashes.

If you want the function to return a pointer to an array, you need to dynamically allocate it, or pass in a buffer (and the buffer's size) for the function to write into.

Upvotes: 1

Mahesh
Mahesh

Reputation: 34625

You are returning the reference of a local variable which is what causing the problem.

char amount_array_n[25];

amount_arra_n is a character array residing on stack which gets invalidated up on return of the function call.

Upvotes: 2

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