Reverse a c-type string

Question

Here is my code:

    void reverseStr(char *str)
{
    if (str == NULL) return;
    int i=0, j=strlen(str) -1;
    while(i<j)
    {
        char temp = str[j];  //i think this is the cause of the problem
        str[j] = str[i];
        str[i] = temp;
        i++;
        j--;
    }
}

So here is where it is called:

int main()
{   
    char *str = "Forest Gump";
    reverseStr(str);
    cout << str;
}

Here is my error:

/Applications/TextMate.app/Contents/SharedSupport/Bundles/C.tmbundle/Support/bin/bootstrap.sh: line 7: 1931 Bus error "$3".out

Any thoughts? Thanks in advance.

It looks like TextMate crashed. Why do you think *your* source code had anything to do with that? Have you tried your code with some other editor? Does your code compile with the command-line C compiler? What about via XCode? — Rob Kennedy, Aug 16 '10 at 20:29
When you've posted the calling code we'll know whether this is a duplicate of http://stackoverflow.com/questions/2345584/reversing-a-string-in-c . — CB Bailey, Aug 16 '10 at 20:30
just a style comment, I would use a for loop instead of a while loop. Also, I think your method will break for symmetric strings. And this should probably be tagged C and not C++ or else you should just use a std::string — Falmarri, Aug 16 '10 at 20:30
It would do to mention that this algorithm and the one @Charles mentions will fail globalization tests. If you're interested in details, check out http://msmvps.com/blogs/jon_skeet/archive/2009/11/02/omg-ponies-aka-humanity-epic-fail.aspx. — kbrimington, Aug 16 '10 at 20:32
@Rob Kennedy: Presumably he's using textmate as an IDE to kick off his built code. bootstap.sh? — CB Bailey, Aug 16 '10 at 20:34
When I ran this code my computer caught fire and then exploded my house :( — Brian R. Bondy, Aug 16 '10 at 20:42
This is decidedly not C. C doesn't use `<<` to mean anything but left-shift. — nmichaels, Aug 16 '10 at 20:45
My compiler (gcc 4.2) gives me a warning when I try to assign a literal to a non-const char*: "deprecated conversion from string constant to ‘char*’". As you obviously use C++ (cout), I wonder if your compiler didn't give you that warning or if you just ignored it? — Frank Osterfeld, Aug 17 '10 at 06:31
Possible duplicate of [Reverse C-style String? - C++](https://stackoverflow.com/questions/2197412/reverse-c-style-string-c) — ivan_pozdeev, Aug 18 '18 at 16:56

score 8 · Accepted Answer · answered Aug 16 '10 at 20:31

8

Str pointes to a fixed string. You are modifying it in place. In other words, you trying to change the text literal. Try this:

char *str = strdup("Forest Gump"); 
reverseStr(str); 
cout << str; 
free(str);

answered Aug 16 '10 at 20:31

James Curran

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Or just `char str[] = "Forest Gump";` removing the need to memory allocation and management. – TheUndeadFish Aug 16 '10 at 20:40

score 4 · Answer 2 · answered Aug 16 '10 at 20:30

4

String literals are read only memory, you can't reverse them, nor modify them in any way without encountering undefined behavior.

Copy your string into a buffer first, then pass in the buffer. Or declare an array instead of a pointer and initialize that array with a string initializer.

answered Aug 16 '10 at 20:30

Brian R. Bondy

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No, since `i > j` in that case – palswim Aug 16 '10 at 20:31
@palswim: I changed my answer I realized that right after I posted it. – Brian R. Bondy Aug 16 '10 at 20:32
in fact, on Linux with gcc, it SIGSEGVs on the line str[j] = str[i]; (where i = 0 and j = 10). – Andre Holzner Aug 16 '10 at 20:41
Yeah, I was about to post the same "answer" right when you did before I realized that the strlen() == 0 error case wouldn't cause problems. – palswim Aug 16 '10 at 20:44

score 0 · Answer 3 · answered Aug 16 '10 at 20:31

0

The error is in a bash/shell script not in your program. Would you please post the bash script also?

answered Aug 16 '10 at 20:31

schoetbi

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Reverse a c-type string

3 Answers3