Trying to reverse a string in place

Question

I am trying to reverse a null terminated string in place in C++. I have written the code below:

//Implement a function to reverse a null terminated string #include<iostream> #include<cstdlib> using namespace std; void reverseString(char *str) { int length=0; char *end = str; while(*end != '\0') { length++; end++; } cout<<"length : "<<length<<endl; end--; while(str < end) { char temp = *str; *str++ = *end; *end-- = temp; } } int main(void) { char *str = "hello world"; reverseString(str); cout<<"Reversed string : "<<str<<endl; }

However, when I run this C++ program , I get a a write access violation inside the while loop at the statement : *str = *end ;

Even though this is fairly simple, I can't seem to figure out the exact reason I am getting this error.

Could you please help me identify the error?

Luchian Grigore · Accepted Answer · 2012-09-07 09:13:54Z

char *str = "hello world";

is a pointer to a string literal, and can't be modified. String literals reside in read-only memory and attempting to modify them results in undefined behavior. In your case, a crash.

Since this is clearly an assignment, I won't suggest using std::string instead, since it's good to learn these things. Use:

char str[] = "hello world";

and it should work. In this case, str would be an automatic-storage (stack) variable.

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