Error malloc on string from argv

Question

I'm using a string received from the arg to return another string with characters shuffled.

int size = strlen(argv[4]);
char* res = malloc(size+1);

Then res is filled with the characters of argv[4], but when I type 'test' in the console, it returns 'Test?' (when I'm not shuffling the letters but just copying the string, character by character).

Why is that ?

If I put size+100 instead, it works, but I don't get why.

How are you copying the string ? Are you including the `\0` ? — cnicutar, Sep 30 '13 at 21:01
Indeed, I forgot to include the \0, it is corrected now, but that was not the problem. Thanks ! — Théo Winterhalter, Sep 30 '13 at 21:28
@Sheeft Check the comments and edit to your accepted answer - it was wrong, but it may be masking your actual problem. — Nigel Harper, Sep 30 '13 at 21:45
@NigelHarper The exact same way +100 was originally masking the problem. — cnicutar, Sep 30 '13 at 21:49
_when I type 'test' in the console .... _ Could you show all arguments supplied to the program? You play with 4-th = argv[4]. Is argv[1], argv[2], argv[3] ok? — sg7, Jun 13 '16 at 23:24

score -2 · Answer 1 · 2013-09-30T21:56:23.703

-2

That is because you did not take into account what the size of char is. This should do the trick:

char* res = (char*)malloc((size+1)*sizeof(char))

edited Sep 30 '13 at 21:56

answered Sep 30 '13 at 21:10

Oh yeah thanks, I used sizeof(char) instead of sizeof(char*)… I indeed did the trick ! – Théo Winterhalter Sep 30 '13 at 21:18
2

Why would you multiply by `sizeof(char *)` ? This is most definitely not the right answer. – cnicutar Sep 30 '13 at 21:29
2

Since sizeof(char) is always 1 your edited answer is exactly equivalent to what the OP had, so it's not an answer. – Nigel Harper Sep 30 '13 at 21:43
Aww right, but now I don't get why it doesn't work the way it is… – Théo Winterhalter Oct 01 '13 at 17:14
I don't get how, but it seems the problem is corrected (I returned to the way it was) now. It's weird ! Thank you for your answers. – Théo Winterhalter Oct 01 '13 at 18:39

Error malloc on string from argv

1 Answers1