(part 5) Han from China answers your C questions

[Borked Pseudo Mailed]

a question abou "atoi"
66650...@qq.com said:

First,thanks for all who have answered my last question.
>
>if char string[20]="12345";
>
>how could I convert the string[2](that is "3") to an int by using
>atoi? I only want to convert string[2],not other string[i].

int a;
char string[20]="12345";

atoi((a=string[2]-'0',"X"));


Yours,
Han from China

[Ben Bacarisse]

Re: (part 5) Han from China answers your C questions

Borked Pseudo Mailed <nobody@pseudo. borked.netwrite s:

a question abou "atoi"
66650...@qq.com said:

>First,thanks for all who have answered my last question.
>>
>>if char string[20]="12345";
>>
>>how could I convert the string[2](that is "3") to an int by using
>>atoi? I only want to convert string[2],not other string[i].

>
int a;
char string[20]="12345";
>
atoi((a=string[2]-'0',"X"));

The consensus is that this exhibits undefined behaviour (quite apart
from being silly). If the OP really needs to use atoi to do this
simple conversion, the easiest way would probably be:

a = atoi((char []){string[2], 0});

--
Ben.

[Peter Nilsson]

Re: (part 5) Han from China answers your C questions

Ben Bacarisse <ben.use...@bsb .me.ukwrote:

Borked Pseudo Mailed <nob...@pseudo. borked.netwrite s:

a question abou "atoi" 66650...@qq.com said:

First,thanks for all who have answered my last question.
>
if                    char string[20]="12345";
>
how could I convert the string[2](that is "3") to an
int by using atoi? I only want to convert string[2],not
other string[i].

    int a;
    char string[20]="12345";
    atoi((a=string[2]-'0',"X"));

>
The consensus is

"You don't vote for kings!"
- King Arther - Monty Python's Holy Grail

that this exhibits undefined behaviour
(quite apart from being silly).

Silly, yes, ub no. Note: atoi("X") produces 0. UB occurs
if (and only if) strtol(blah, 0, 10) would produce a value
outside the range of int.

 If the OP really needs to use atoi to do this
simple conversion,

The OP doesn't, so why entertain the possibility? ;)

--
Peter

[Ben Bacarisse]

Re: (part 5) Han from China answers your C questions

Peter Nilsson <airia@acay.com .auwrites:

Ben Bacarisse <ben.use...@bsb .me.ukwrote:

>Borked Pseudo Mailed <nob...@pseudo. borked.netwrite s:

a question abou "atoi" 66650...@qq.com said:
First,thanks for all who have answered my last question.
>
if                    char string[20]="12345";
>
how could I convert the string[2](that is "3") to an
int by using atoi? I only want to convert string[2],not
other string[i].
>
    int a;
    char string[20]="12345";
    atoi((a=string[2]-'0',"X"));

>>
>The consensus is

>
"You don't vote for kings!"
- King Arther - Monty Python's Holy Grail
>

>that this exhibits undefined behaviour
>(quite apart from being silly).

>
Silly, yes, ub no. Note: atoi("X") produces 0. UB occurs
if (and only if) strtol(blah, 0, 10) would produce a value
outside the range of int.

Well I agree in that that has always been my reading of the matter. I
should have said that this has been debated.

--
Ben.