Question

I have the following C code fragment and have to identify the error and suggest a way of writing it more safely:

char somestring[] = "Send money!\n";
char *copy;

copy = (char *) malloc(strlen(somestring));

strcpy(copy, somestring);
printf(copy);

So the error is that strlen ignores the trailing '\0' of a string and therefore it is not going to be allocated enough memory for the copy but I’m not sure what they’re getting at about writing it more safely?

I could just use malloc(strlen(somestring)+1)) I assume but I’m thinking there must be a better way than that?

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EDIT: OK, I’ve accepted an answer, I suspect that the strdup solution would not be expected from us as it’s not part of ANSI C. It seems to be quite a subjective question so I’m not sure if what I’ve accepted is actually the best. Thanks anyway for all the answers.

Answer 1

char   somestring[] = "Send money!\n";
char   *copy;
size_t copysize;

copysize = strlen(somestring)+1;
copy = (char *) malloc(copysize);
if (copy == NULL)
    bail("Oh noes!\n");

strncpy(copy, somestring, copysize);
printf("%s", copy);

Noted differences above:

• Result of malloc() must be checked!
• Compute and store the memory size!
• Use strncpy() because strcpy() is naughty. In this contrived example it won’t hurt, but don’t get into the habit of using it.

EDIT:

To those thinking I should be using strdup()… that only works if you take the very narrowest view of the question. That’s not only silly, it’s overlooking an even better answer:

char somestring[] = "Send money!\n";
char *copy = somestring;
printf(copy);

If you’re going to be obtuse, at least be good at it.