自写atoi----字符串转化为整形

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字符串转化为整形的各类情况：

char *str1 = "12345"; //普通
char *str2 = "+12345"; //正数
char *str3 = "-12345"; //负数
char *str4 = " 12345"; //前面有若干个空格
char *str5 = " 1 2 3 4 5"; //数字间存在空格
char *str6 = "0x12345"; //十六进制
char *str7 = "012345"; //八进制
char *str8 = "abc123"; //含其他字符

char *str2 = "+12345"; //正数
char *str3 = "-12345"; //负数
char *str4 = " 12345"; //前面有若干个空格
char *str5 = " 1 2 3 4 5"; //数字间存在空格
char *str6 = "0x12345"; //十六进制
char *str7 = "012345"; //八进制

char *str8 = "abc123"; //含其他字符

代码如下：

#include<stdio.h>int my_atoi(const char *str){int result = 0;      //存放转换后的值int sign = 1;        //符号位int weight = 10;     //权值（十进制，八进制，十六进制）while(*str != '\0'){if(*str == '+')  //表明是正数{sign = 1;str++;       //将'+'掠过}if(*str == '-')  //表明是负数{sign = -1;str++;       //将'-'掠过 }/*if(*str == '0' && *(++str) != 'x'){weight = 8;  //注意！！！！！：此处不能加str++，否则会错失一个字符//str++；   因为执行完*(++str) != 'x'后,str已经指向一个未完全判断的字符（虽然不等于x）}if(*str == '0' && *(++str) == 'x')//表明是16进制{weight = 16;str++;       //将'x'掠过}*/if(*str == '0'){if(*(str + 1) == 'x'){  weight = 16;str += 2;  //将'0'和'x'掠过}else{weight = 8;str += 1;  //将'0'掠过}}if(*str >= '0' && *str <= '9'){result = result * weight + (*str - '0');str++;}else{str++;//非有效字符全部掠过（+ - 0x x exp）}}return result * sign;}int main(){char *str1 = "12345";     //普通char *str2 = "+12345";    //正数char *str3 = "-12345";    //负数char *str4 = "   12345";  //前面有若干个空格char *str5 = " 1 2 3 4 5";//数字间存在空格char *str6 = "0x12345";   //十六进制char *str7 = "012345";    //八进制char *str8 = "abc123";printf("%6d\n",my_atoi(str1));printf("%6d\n",my_atoi(str2));printf("%6d\n",my_atoi(str3));printf("%6d\n",my_atoi(str4));printf("%6d\n",my_atoi(str5));printf("%6d\n",my_atoi(str6));printf("%6d\n",my_atoi(str7));printf("%6d\n",my_atoi(str8));return 0;}

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