Improve company productivity with a Business Account.Sign Up

x
  • Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 597
  • Last Modified:

String literals in C++

The following program seg faults on my machine.

int main() {
    char *cp = "Hell";
    *cp = 'B';
}

while the following works fine.

int main() {
    char cp[] = "Hell";
    *cp = 'B';
}

The following program does not compile.

int main() {
    const char *cp = "Hell";
    *cp = 'B';
}

Can someone explain the three observations?
0
priyendra
Asked:
priyendra
1 Solution
 
AlexFMCommented:
1) cp points to read-only memory where program string constants are kept. Changing of this memory is access violation.
2) cp points to char aray allocated on stack. It is possible to change this memory.
3) *cp is constant pointer, *cp = ... is not allowed.
0
 
priyendraAuthor Commented:
Alex, thanks a lot for your answer. I guess this must be one of the fastest answers I have ever obtained in EE :-) For my other question, I shall await a few more comments before closing.
0
 
AxterCommented:
FYI:
Not all compilers will put string literals in read-only memory.

Changing the contents of a string literal results in undefined behavior IAW with the C++ standards.

Some compilers will allow you to do this, and others will not.
For example, VC++ 5.0 will allow you to change the contents of a pointer to a string literal.
However, VC++ 6.0/7.x will not.


You should avoid code that results in undefined behavior.
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Get expert help—faster!

Need expert help—fast? Use the Help Bell for personalized assistance getting answers to your important questions.

Tackle projects and never again get stuck behind a technical roadblock.
Join Now