atoi function in C++

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4.00/5 (2 votes)

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Hi,

I came across C++ function

atoi

, This function returns integer representation of given string.

If i pass "987" to this function , it will return 987 as integer.

In MSDN it is written that, this function returns 0 on failure. What if i pass "0" to this function ??

it will return 0 as integer .....Should i treat it as a ERRORCODE or converted value :(

Posted 21-Jun-12 0:38am

PrafullaVedante

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Eugen Podsypalnikov 21-Jun-12 6:54am

// In MSDN it is written that, this function returns 0 on failure.

Please try it :) :
assert(12 == atoi("12 months"));

2 solutions

Solution 1

When the function returns 0, you must check yourself if the string is a valid number (parse for optional leading white spaces, optional sign, and the '0' character followed by a NULL byte).

If you need advanced error checking, you may use the strtol() [^] function.

Posted 21-Jun-12 0:44am

Jochen Arndt

Updated 21-Jun-12 0:45am

v2

Comments

PrafullaVedante 21-Jun-12 6:47am

strtol also has same problem.

Jochen Arndt 21-Jun-12 6:54am

Not when passing the endptr parameter and check if it is equal to nptr (not a number) or points to an invalid termination character (not NULL, trailing white spaces may be optional allowed). strtol also provides checks for overflow and underflow conditions via return value and errno.

nv3 21-Jun-12 8:27am

I fully agree. For serious business, always use strtol and not atoi. +5

BillW33 21-Jun-12 10:16am

Good answer Jochen, +5.

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iSuperRay · Accepted Answer · 2012-06-21T04:48:00

You can use errno global variable. If it is not equal to 0 then there was error and you can check what it was (overflow or other conversion error)
In the case atoi returns 0 and errno == 0 you can be sure that conversion was finished successfully

Something like this:

C++

int val;

val = atoi("bad value");
if (errno != 0)
{
   printf("Error");
}
else
{
   // Do something with val
}