1+ #include <stdio.h>
2+ #include <string.h>
3+ #include <limits.h>
4+
5+
6+ static int intToString (int i ,char * arr ){
7+ int t_len = sprintf (arr ,"%d" ,i );
8+ arr [t_len ]= '\0' ;
9+ return t_len ;
10+ }
11+ static int myStrcmp (char * start ,char * end ,char * other ){
12+ for (char * c1 = start ,* c2 = other ;c1 <=end && c2 != '\0' ;c1 ++ ,c2 ++ ){
13+ if (* c1 > * c2 ){
14+ return 1 ;
15+ }else if (* c1 < * c2 ){
16+ return -1 ;
17+ }
18+ }
19+ return 0 ;
20+ }
21+
22+ int myAtoi (char * str ) {
23+ int is_negative = 0 ;
24+ char * start = NULL ,* end = NULL ;
25+ for (char * c = str ;c != '\0' ;c ++ ){
26+ if (start == NULL && (* c == ' ' || * c == '\n' || * c == '\t' )){
27+ continue ;
28+ }else if ((* c == '-' || (* c >='0' && * c <='9' )|| * c == '+' )&& start == NULL ){
29+ start = c ;
30+ if (* c == '-' ){
31+ is_negative = 1 ;
32+ }
33+ }else if (* c >='0' && * c <='9' && start != NULL ){
34+ end = c ;
35+ }else {
36+ break ;
37+ }
38+ }
39+
40+ if (start == NULL ){
41+ return 0 ;
42+ }else if (end == NULL ){
43+ end = start ;
44+ }
45+
46+ if (* start == '+' ){
47+ start ++ ;
48+ }
49+
50+ // printf("%c:%c\n",*start,*end);
51+ //检查是否越界
52+ int result_len = end - start + 1 ;
53+ if (is_negative ){
54+ char min_str [40 ];
55+ int min_len = intToString (INT_MIN ,min_str );
56+ if (result_len > min_len || (result_len == min_len && myStrcmp (start ,end ,min_str )> 0 )){
57+ return INT_MIN ;
58+ }
59+ }else {
60+ char max_str [40 ];
61+ int max_len = intToString (INT_MAX ,max_str );
62+ if (result_len > max_len || (result_len == max_len && myStrcmp (start ,end ,max_str )> 0 )){
63+ return INT_MAX ;
64+ }
65+ }
66+
67+ int result = 0 ;
68+
69+ // printf("%c:%c",*start,*end);
70+ for (char * c = start ;c <=end ;c ++ ){
71+ if (* c != '-' && * c != '+' ){
72+ result *=10 ;
73+ result += (* c - '0' );
74+ }
75+ }
76+
77+ if (* start == '-' ){
78+ result = - result ;
79+ }
80+ return result ;
81+ }
82+
83+
84+ int main (){
85+ printf ("%d\n" ,myAtoi ("+1231312" ));
86+ printf ("%d\n" ,myAtoi (" -11919730356x" ));
87+ printf ("%d\n" ,myAtoi (" +1146905820n1" ));
88+ printf ("%d\n" ,myAtoi ("1" ));
89+ printf ("%d\n" ,myAtoi ("123" ));
90+ printf ("%d\n" ,myAtoi ("-1231312" ));
91+ printf ("%d\n" ,myAtoi ("-1231312fqwef" ));
92+ printf ("%d\n" ,myAtoi ("-1231312 992" ));
93+ printf ("%d\n" ,myAtoi ("3000000001" ));
94+ printf ("%d\n" ,myAtoi ("-3000000001" ));
95+ printf ("%d\n" ,myAtoi ("wefwqef-3000000001" ));
96+ printf ("%d\n" ,myAtoi (" -3000000001" ));
97+ return 0 ;
98+ }
