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Thinking in C++
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Character array literals

The place where strict constness is not enforced is with character array literals. You can say

char* cp = "howdy";

and the compiler will accept it without complaint. This is technically an error because a character array literal (“howdy” in this case) is created by the compiler as a constant character array, and the result of the quoted character array is its starting address in memory. Modifying any of the characters in the array is a runtime error, although not all compilers enforce this correctly.

So character array literals are actually constant character arrays. Of course, the compiler lets you get away with treating them as non-const because there’s so much existing C code that relies on this. However, if you try to change the values in a character array literal, the behavior is undefined, although it will probably work on many machines.

If you want to be able to modify the string, put it in an array:

char cp[] = "howdy";

Since compilers often don’t enforce the difference you won’t be reminded to use this latter form and so the point becomes rather subtle.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire