Segmentation fault when trying to modify a string

Question

This code is giving me a segmentation fault at run time.

char *str = "HELLO";
str[0] = str[2];

Please can anyone tell me why?

Who is upvoting this ? Not a bad question but stackexchange will reach the point where it will detect this question and be able to point users at the c-faq. — cnicutar, May 27 '11 at 08:11

score 7 · Answer 1 · answered May 27 '11 at 07:18

7

You cannot modify the contents of a string literal. Put it in a character array if you wish to be able to do so.

char str[] = "HELLO";
str[0] = str[2];

answered May 27 '11 at 07:18

Jeff Mercado

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score 7 · Answer 2 · answered May 27 '11 at 07:19

7

You're getting a seg-fault because the compiler has placed the string constant "HELLO" into read-only memory - and attempting to modify the string is thus failing.

answered May 27 '11 at 07:19

Will A

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score 4 · Answer 3 · answered May 27 '11 at 08:01

4

This is compiled to a string literal in the read only section.

        .section        .rodata
.LC0:
        .string "HELLO"

answered May 27 '11 at 08:01

Santhosh

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score 3 · Accepted Answer · answered May 27 '11 at 07:53

3

Standard does not allow modifying a string literal. The string is stored in a readonly segment of the program, for example in linux, it is stored in the .rodata section of the executable which cannot be written.

answered May 27 '11 at 07:53

phoxis

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Segmentation fault when trying to modify a string

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