Why does printf convert large numbers?

Question

Why doesn't this work?

printf("%d \n\n\n\n", atoi("11110010100"));

it outputs -1774891788... I just want it outputted as it is. It seems to work just fine if the number is a bit smaller.

Why do you assume the problem is with `printf` and not with `atoi`? — Oliver Charlesworth, May 09 '15 at 11:42
`11110010100` in base 10 converts to base 2 as `1010010110001101010100110011110100` (34 bits) — pmg, May 09 '15 at 11:43

score 4 · Accepted Answer · answered May 09 '15 at 11:42

4

atoi returns an int. You pass a string which contains a number bigger than what int(in your implementation) can hold. So, you have an integer overflow.

To print the maximum value an int can hold, include limits.h and print INT_MAX.

answered May 09 '15 at 11:42

Spikatrix

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could you elaborate on how you would use INT_MAX? – something May 09 '15 at 11:49
`printf("%i",INT_MAX);` when you've included `limits.h` – Spikatrix May 09 '15 at 11:57

score 1 · Answer 2 · answered May 09 '15 at 11:59

1

int atoi (const char * str) convert string to integer,and the basic signed integer type capable of containing at least the [−32767,+32767] range,

the 11110010100 is bigger than integer storage capability, so you have an overflow.

you can try this method to parse a String to a Double: atof
http://www.lemoda.net/c/string-to-double/

answered May 09 '15 at 11:59

Yacino

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It would be exceptional to find a system using a two byte integer type these days. – David Hoelzer May 09 '15 at 12:00
No, kamel is right: according to K&R, **2.2 Data Types and Size**, "ints are *at least* 16 bits" (see also http://stackoverflow.com/a/11438985/2564301). And `atoi` returns an `int`. – Jongware May 09 '15 at 13:49

Why does printf convert large numbers?

2 Answers2