Array initialization without comma

Question

In the following code I am having the output like(last one giving segmentation fault)

 U   
 s    
 HelloThisisatest    
 Segmentation fault (core dumped)

but i do not understand why. code is

int main()
{
   char *a[]={"Hello" "This" "is" "a" "test"};
   printf("%c\n",a[1][0]);
   printf("%c\n",a[0][8]);
   printf("%s\n",a[0]);
   printf("%s\n",a[3]);
   return 0;
}

Another question is that can we initialize an 2-D array without using comma? Another situation that I got that when i am replacing the \ns by \ts then output changes like

"U s HelloThisisatest (null)"

why?

Answer 1

This is because in C, two adjacent strings are concatenated into one. So "Hello" "World" is actually a single string "HelloWorld".

• In your case The array of pointer actually contains one single string "HelloThisisatest". In the first printf you are accessing the location 1, which is undefined behaviour.

• The next printf accesses the character 8 of the string which is s .

• The third printf prints the entire string stored on the location 0, which is "HelloThisisatest"

• The last printf attempts to access the array location 3, which is undefined behavour, as it is not initialized.

EDIT

Refer C11/C99 standard Section 5.1.1.2 Paragraph 6, which tells:

Adjacent string literal tokens are concatenated.