Atoi implementation, atoi implementation

Atoi implementation, atoi implementation

The processing policy completely imitates C language library functions

Overflow handling policy:

Output upper or lower bound (2147483647 and-2147483648)

Test data:

Char * s1 = "\ t \ f \ v \ n \ r-00100 \ n \ t \ f \ v \ n \ r1234"; char * s2 = "-- 099 "; char * s3 = "nas"; char * s4 = "+ 2147483647sc"; char * s5 = "20.0sc"; char * s6 = "20-1sc "; char * s7 = "0-099"; char * s8 = "-9999999999999999999"; // overflow char * s9 = "+ 9999999999999999999 ";

Processing result:

The first behavior is the library function result, and the second behavior is the My_atoi result.

Code implementation:

# Pragma once # include <iostream> using namespace std; int My_atoi (const char * pstr) // The content pointed to by the pointer cannot be changed, the pointer cannot be changed to char * const pstr {if (! Pstr) {printf ("Pointer is NULL \ n"); return 0;} unsigned int result = 0; // use unsigned to handle int sign = 1; // The flag. The default value is int out = false. // aoti () requires that the first digit or symbol must be a number with the last digit or symbol, when the first digit or symbol is met, the value out = true, and then the non-digit exit while (* pstr) {if (* pstr> '9' | * pstr <'0') // if (out) return result * sign is returned if a non-number is returned after conversion; if (* pstr = '-') {sign =-1; out = true;} else if (* pstr = '+') out = true; else if (* pstr <= '9' & * pstr> = '0') {result = res Ult * 10 + * pstr-'0'; // returns the upper and lower bounds if (result> = 2147483647 & sign = 1) return 2147483647; if (result> = 2147483648 & sign =-1) // if result * sign> 2147483648 is written, the binary value of 2147483648 is automatically expressed (unsigned ), // convert the expression to a signed integer of 100000 after comparison with int... that is,-2147483648. Therefore, the unsigned int is used here. // If int is used, the value 2147483648 is changed to-2147483648 for comparison, and the maximum value of int Is 2147483647. Even if it remains unchanged, the return-2147483647-1 is not applied; // cannot be written as-2147483648out = true;} else if (* pstr! = ''& * Pstr! = '\ N' & * pstr! = '\ R' & * pstr! = '\ T' & * pstr! = '\ V' & * pstr! = '\ F') // return result * sign; pstr ++;} return result * sign;} void main () {char * s1 = "\ t \ f \ v \ n \ r-00100 \ n \ t \ f \ v \ n \ r1234"; char * s2 = "-- 099 "; char * s3 = "nas"; char * s4 = "+ 2147483647sc"; char * s5 = "20.0sc"; char * s6 = "20-1sc "; char * s7 = "0-099"; char * s8 = "-9999999999999999999"; // overflow char * s9 = "+ 9999999999999999999"; int i1 = atoi (s1 ); int i2 = atoi (s2); int i3 = atoi (s3); int i4 = atoi (s4); int i5 = atoi (s5); int i6 = atoi (s6 ); int i7 = atoi (s7); int i8 = atoi (s8); int i9 = atoi (s9 ); cout <i1 <''<i2 <'' <i3 <''<i4 <'' <i5 <''<i6 <<''<i7 <'' <i8 <''<i9 <endl; i1 = My_atoi (s1); i2 = My_atoi (s2); i3 = My_atoi (s3); i4 = My_atoi (s4); i5 = My_atoi (s5 ); i6 = My_atoi (s6); i7 = My_atoi (s7); i8 = My_atoi (s8); i9 = My_atoi (s9 ); cout <i1 <''<i2 <'' <i3 <''<i4 <'' <i5 <''<i6 <<''<i7 <'' <i8 <''<i9 <endl; int a = 2147483648; cout <a <endl; //-2147483648 system ("pause ");}