Program aborts when using strcpy on a char pointer? (Works fine on char array)

Question

I\'m perplexed as to why the following doesn\'t work:

char * f = \"abcdef\";
strcpy(f, \"abcdef\");
printf(\"%s\",f);

char s[] = \"ffffd\";
strcpy(&s[0],          


        

Answer 1

The statement char * f = "abcdef" assigns a point in memory to the literal string "abcdef", however it will refuse to let you modify its contents until the memory is dynamically allocated - it's equivalent to a const char.
All you're doing is creating a pointer in memory and then writing over the next 6 bytes, which is illegal in C.

Answer 2

"abcdef" and "ffffd" are string literals which may reside in a read-only section of your address space. char s[] = "ffffd" ensures this literal is copied to stack - so it's modifiable.

Answer 3

In the first example, you have a pointer to a string literal. This pointer should really be const char *, because any attempt to modify a string literal is undefined behaviour. However, for legacy reasons allows you to use a char * to point at it. But you still shouldn't be trying to modify it.

In the second version, you have a bog-standard array, whose contents happen to be initialised to be equivalent to your string. This is modifiable, as it's your array.

Answer 4

The first example is a char * to a character literal (a literal is "something"). Character literals are read-only, and attempting to write to them can result in crashes. Your first pointer should really be const char *f = "abcdef";, which strcpy won't take.

Answer 5

String literals are considered readonly by most compilers, so the memory where they reside can be marked as readonly, resulting in a runtime error.

To make it work, do the following:

char * f = strdup("abcdef");
strcpy(f, "abcdef");
printf("%s",f);
free(f);

This creates a modifiable copy of the string in the heap memory, which needs to get freed at the end of your program of course.

Answer 6

char * f = "abcdef"; defines a char pointer to "abcdef" which is located in read-only area so you can't write to this place

char s[] = "ffffd"; defines a char array on the stack which is writable.