Converting Char Array to Integer

Question

I fall into a interesting problem. When I first call string_to_int, stack created a memory buffer for size 6, and converted to a correct integer. But at the second call, IMO, stack reused the buffer (because smaller than size 6?), i still see content " 513" at the break point, so atoi converted to 56513 instant of 56.

How should I do array to int properly and fast ? I can't use strtoi, or stoi because the array can be sometimes fill by space only. i can't directly pass the array to atoi because the array (char stream from network), for example, can be "123456" but it actually contain 2 separate values "123" and "456"

    static int string_to_int(const char* number, int size)
    {
        char stackbuf[size];
        memcpy(stackbuf, number, size);
        return atoi(stackbuf);
    }

char* ptr1 = "   513"

string_to_int(ptr1, 6); //result = 513

char* ptr2 = "056"

string_to_int(ptr2, 3); //result = 56513

Since you're using C++, why not just use stringstream? That way you avoid manual memory management and legacy C APIs. — MrEricSir
– MrEricSir, Commented Oct 9, 2015 at 4:13

Iharob Al Asimi · Accepted Answer · 2015-10-09 03:27:18Z

3

You need the nul terminator for atoi to work correctly, try strcpy() instead of memcpy() or copy size + 1 bytes.

edited Oct 9, 2015 at 3:27

answered Oct 9, 2015 at 3:11

Iharob Al Asimi

53.1k6 gold badges66 silver badges100 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

vishal Over a year ago

strncpy is a good option as it will also prevent from buffer overflow

chux Over a year ago

@vishal strncpy() has its chance of mis-use too as it does not insure the the string end with '\0'. Exactly the same problem OP is having here.

Foon · Accepted Answer · 2015-10-09 03:29:29Z

2

As noted by iharob, the issue is that in your 2nd case, you don't have a null-terminated string for atoi to work with.

static int string_to_int(const char* number, int size)
    {
        char stackbuf[size+1];
        memcpy(stackbuf, number, size);
        stackbuf[size] = '\0'; //or you could use strncpy
        return atoi(stackbuf);
    }

edited Oct 9, 2015 at 3:29

answered Oct 9, 2015 at 3:23

Foon

6,51811 gold badges42 silver badges45 bronze badges

3 Comments

Foon Over a year ago

Sorry about that (or if you prefer <voice=SeanConnery>Something something, in the latin alphabet, Jehovah starts with an i</voice>)

A.S.H Over a year ago

He didnt have the terminating zero for the first case neither (there are 3 leading spaces). The zero was there out of luck

chux Over a year ago

Using strncpy() in this context provides no benefit.

Collectives™ on Stack Overflow

Converting Char Array to Integer

2 Answers 2

2 Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related