C语言中atoi()函数实现--字符串转int型整数

#include <iostream>
#include <string>

enum Status{kValid = 0, kInValid}; //全局变量，用于记录返回0时，是正常退出还是出现异常。
int g_nStatus = kValid;

long long str2intCore(const char* digit, bool minus){

long long num = 0;
while(*digit != '\0'){
if(*digit - '0' >= 0 && *digit - '0' <= 9){
int flag = minus == false ? 1:-1;
num = num*10+ flag*(*digit-'0');

if((!minus && num > 0x7FFFFFFF) || (minus && num < (signed int)0x80000000)){ //判断是否超过int的表示范围
num = 0;
break;
}
digit++;

}else{
num = 0;
break;
}
}

if(*digit=='\0'){           //判断是否正常结束
g_nStatus = kValid;
}
return num;
}

int str2int(const char* str){
g_nStatus = kInValid;
long long num = 0;
if(str!=NULL && *str!='\0'){
bool minus = false;
if(*str == '+'){
str++;
}
if(*str == '-'){
minus = true;
str++;
}

if(*str != '\0'){
num = str2intCore(str, minus);
}

}

return (int)num;
}

int main(int argc, const char * argv[]) {
// insert code here...

char str[] = "-1234433";
std::cout << str2int(str) << std::endl;
return 0;
}