Implementation of the database function atoi () and the implementation of the database function atoi

Implementation of the database function atoi () and the implementation of the database function atoi

Int atoi (const char * nptr );

IfThe first non-space characterYes. If it is a number or plus or minus sign, type conversion is started. If it is detected that the conversion is not a number (including the terminator \ 0), the conversion is stopped and the integer number is returned. Otherwise, zero is returned.

Note: If the string is illegal input: the string is null, and only one '+' or '-', non-number, and so on, returns the integer 0; if the input value is "0", the return value is the integer value 0. In this case, atoi () is distinguished by a global variable. Another point: for example, if the input is "123abc", atoi () can also be correctly executed and the number of integer values is 123.

Enum Status {kValid = 0, kInvalid}; int g_nStatus = kValid; int StrToInt (const char * str) {g_nStatus = kInvalid; long num = 0; if (str! = NULL & * str! = '\ 0') {bool minus = false; if (* str =' + ') str ++; else if (* str = '-') {str ++; minus = true;} if (* str! = '\ 0') {num = StrToIntCore (str, minus) ;}} return (int) num;} long StrToIntCore (const char * digits, bool minus) {long num = 0; const char * digit = digits; while (* digit! = '\ 0') {if (* digit> = '0' & * digit <= '9') {int flag = minus? -1: 1; num = num * 10 + flag * (* digit-'0'); if ((! Minus & num> 0x7FFFFFFF) | (minus & num <(signed int) 0x80000000) // check whether overflow exists {num = 0; break ;} digit ++;} else {// num = 0; break ;}} if (* digit = '\ 0' | digit-digits> 0) {g_nStatus = kValid;} return num ;}

Refer to offoffer

Int atoi (char * s) without C/C ++ library functions)

Int Atoi (char * s) {int Int = 0, I; for (I = 0; * (s + I )! = '\ 0'; I ++) {if (* (s + I) <'0' | * (s + I)> '9') return Int; int = Int * 10 + (* (s + I)-'0');} return Int;
}

Int atoi (char * s) without C/C ++ library functions)

# Include <stdio. h>
# Include <string. h>

Int atoi (char * s)
{
Int I, j, k, len, value = 0;
Int flag = 1;

Len = strlen (s );
J = 0;
For (I = 0; I <len; I ++)
{
If (s [I]! = ''& S [I]! = '\ T ')
{
S [j] = s [I];
J = j + 1;
}
}
S [j] = '\ 0 ';
If (j = 0) return 0;
K = 0;
If (s [0] = '-')
{
Flag =-1;
K = 1;
}
Else if (s [0] = '+ ')
{
Flag = 1;
K = 1;
}

For (I = k; I <j; I ++)
{
Value = value * 10 + s [I]-'0 ';
}

Value = flag * value;
Return value;
}

Void main ()
{
Char s [10] = "-12345 ";
Int n;

N = atoi (s );
Printf ("% d \ n", n );
}