I'm new to C++ and I'm playing with pointers. I can't figure out why this piece of code doesn't work for me. Can you tell me what's wrong with it?
char * name = "dharman";
char *ptr = name+3;
*ptr = 'a';
printf("%s", name);
I get unhandled exception all the time.
This alone is an error:
char * name = "dharman";
The string is in constant memory but the pointer's type indicates it can be modified. Attempting to modify it produces undefined behavior: on other platforms the program will work but you got unlucky.
This was a quirk in C++03; the newer C++11 spec makes it illegal. The reason it was ever done was C compatibility.
Whether you're writing in C++ or plain C, the solution is simple:
char name[] = "dharman";
Now the compiler stores the data in read-write memory because you have asked for an array of char, not a pointer to some other memory.
String literals, like "dharman", are read-only and you cannot modify them. Instead, create and initialize an array that is not read only.
char name[] = "dharman";
name is a pointer to a string literal "dharman", which is located in read-only memory.
In your statement *ptr = 'a', you are trying to modify this string literal, which results in Undefined Behavior
It doesn't work because "dharman" is constant, it's a string literal. You cannont change it!
String literals are usually placed in read-only segments of memory.
You are trying to modify a constant string. You need to copy the constant first to some memory that you own. Try this:
char *name = (char*) malloc(10);
memcpy(name, "dharman", strlen("dharman"));
...
You are setting name to point at a const string and then trying to modify it. Copy the string to a modifiable location:
char *name = (char*) malloc(strlen("dharman") + 1);
memcpy("dharman", name, strlen("dharman") + 1);
The reason for unhandled exception in your case is.In your code
char *ptr= name+3;
consider the base address of name as eg:23300, so char *ptr =name+3 will be equal to 23300+(3*sizeof(char)).so now ptr points to 23300+(3*1)=23303.each element occupies one bye for char so ptr will point to letter 'a' in "dharman".since "dharman" is char const you can't its value that's why you are getting error.if u remove the line *ptr=3.the code will work without out any issue.I hope you find this post useful.
