Clear a doubt, Its a task given by trainer.

**Gillljollyyy** · 10-09-2014

Hi
I have a question, please clear my doubt as soon as possible.

In this code, i declared a string constant and trying to print the length of string. I know that if i write char a1[7] or char a1[] than it runs and give aggregate output, but in this case it is giving double length of string.

Code:

#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char a1[6]={"Bhopal"};
clrscr();
printf("%d\n",strlen(a1));
getch();
}

here generated output is 12

So please tell me, what is the reason behind it.

**Matticus** · 10-09-2014

You're not providing enough space in your array for the null character ('\0'), so that char array is not even a string. "strlen()" looks for the null character to determine the end of the string. So it will continue checking characters beyond the bounds of your array until it happens to come across a byte of value '\0'. So the value of 12 you're getting is arbitrary.

Also, the return type of "main()" should be int, not void.

FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[]) - Cprogramming.com

**Gillljollyyy** · 10-09-2014

hi Matticus,
can u tell me, why is this program giving same result. suppose i initialize a string like

Code:

char a1[6]={"Bhopal"};   // here output is 12

char a1[5]={"Bhopa"};   // here output is 10

char a1[4]={"Bhop"};   // here output is 8

these 12, 10, 8 is not a garbage value.
how is compiler working for this code.

**Elkvis** · 10-09-2014

The problem is that you are telling the compiler that you are reserving space for 6 char elements, but the string itself requres 7. You also don't need the curly brackets around the string. You should remove them.

Code:

//Wrong:
char a1[6]="Bhopal";

//Right:
char a1[7]="Bhopal";
//or
char a1[]="Bhopal";

**Matticus** · 10-09-2014

Running past the bounds of your array is undefined behavior. There is no value in trying to reason about undefined behavior.

**Salem** · 10-09-2014

Well whenever you start doing undefined things, there's no telling what 'answers' you're going to get.

Code:

#include <stdio.h>

void memdump ( const char *p, size_t len ) {
  char ascii[17] = { 0 };
  for ( size_t i = 0, c = 0 ; i < len ; i++ ) {
    char b = p[i];
    if ( b >= 32 && b <= 126 ) ascii[c++] = b;
    else ascii[c++] = '.';
    printf("%02x ", (unsigned char)b);
    if ( c == 16 ) {
      printf("%s\n", ascii );
      c = 0;
    }
  }
}

int main(){
  char a1[6]={"Bhopal"};   // here output is 12
  memdump(a1,16);
  char a2[5]={"Bhopa"};   // here output is 10
  memdump(a2,16);
  char a3[4]={"Bhop"};   // here output is 8
  memdump(a3,16);
  return 0;
}

$ gcc -std=c99 foo.c
$ ./a.out 
42 68 6f 70 61 6c 00 00 20 07 40 00 00 00 00 00 Bhopal.. .@.....
42 68 6f 70 61 00 00 00 d0 04 40 00 00 00 00 00 Bhopa.....@.....
42 68 6f 70 ff 7f 00 00 00 b0 7d 1e 63 89 c6 ba Bhop......}.c...

Bhopal and Bhopa would apparently work for me, but I wouldn't call that 'success' because I know the code is wrong.

Thread: Clear a doubt, Its a task given by trainer.

Thread Tools

Search Thread

Display

Clear a doubt, Its a task given by trainer.

Similar Threads

Vector::clear() won't clear

Help from the task

Logic trainer, fill the boxe >summation of two previous numbers

Nim Trainer

How do I determine if a task is i real-time task in schedule()?

Tags for this Thread