Why does value change in string literal

Question

main()
{
  char *c="abhishek";
  int i;
  c[2]=90;
  for(i=0;i<12;i++)
  {
    printf("%c",c[0])
  }
}

Here the output is abZishek. But this should result in a bus error because this is a string literal and we can not change its value. Why does the value of c change?

Modifying a string literal gives undefined behavior, so anything can happen. — Jerry Coffin, Feb 21 '14 at 17:30
This shouldnt even compile, a string literal is of type `const char[]` — Sebastian Hoffmann, Feb 21 '14 at 17:31
This is precisely why you shouldn't use a non-const `char *` to point to a string literal. — chris, Feb 21 '14 at 17:31
Because it's not a __constant__ literal. Use `const char *c`. — Paweł Stawarz, Feb 21 '14 at 17:31
@Paranaix, It shouldn't as of C++11. Before that, it was an exception and AFAIK, all versions of C allow it. — chris, Feb 21 '14 at 17:31
@Paranaix Although deprecated, a conversion from character literal to `char*` existed in C++03. — Angew is no longer proud of SO, Feb 21 '14 at 17:38
I doubt the output will be abZishek if you don't use the loop index. And backup your datas before using it, because accessing with index 9 is UB. — manuell, Feb 27 '14 at 13:52

score 7 · Answer 1 · edited May 23 '17 at 12:28

7

According to section 2.14.5 paragraph § 11 of the C++ standard, it invokes undefined behavior:

The effect of attempting to modify a string literal is undefined.

This means anything can happen and indeed something has happened. You must not make any assumptions about what may happen when you invoke undefined behavior.

edited May 23 '17 at 12:28

Community

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answered Feb 21 '14 at 17:31

4pie0

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Is this rule also true for c or it is applicable only in c++ – user3335653 Feb 22 '14 at 06:28
yes, in C also the behavior is undefined if a program attempts to modify any string literals. – 4pie0 Feb 22 '14 at 13:30

score 3 · Answer 2 · answered Feb 21 '14 at 17:35

3

"Undefined behaviour" does not guarantee a "bus error" or any other sort of error. In general it cannot be easily detected so your compiler is not required to bother. Here, it does not bother. However, in doing this you may cause unpredictable or strange things to happen.

You're also missing library includes and a return type for main; which C++ book are you using?

answered Feb 21 '14 at 17:35

Lightness Races in Orbit

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i did not not include libraries because it is obvious.what is the need to include.I am a final year student in Btech and a want to be a java programmer>and i am certified in java .i want to read c and c++ only up to level that i can pass the written test of compnies.i am using test your c skills in c for practice and head first c for theory.What else i should use?? – user3335653 Feb 22 '14 at 05:29
@user3335653: It's not "obvious" to use at all that you've been including the correct ones if you don't show them to us. Here is your book recommendation: http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list – Lightness Races in Orbit Feb 22 '14 at 15:42

Why does value change in string literal

2 Answers2