剑指Offer-67：把字符串转换成整数

题目：

链接：

思路标签：

解答：

class Solution {
public:
enum Status { kValid = 0, kInvalid };
int g_nStatus = kValid;

int StrToInt(string str) {
g_nStatus = kInvalid;
long long num = 0;
const char* cstr = str.c_str();
if ((cstr != nullptr) && (*cstr != '\0'))
{
int minus = 1;
if (*cstr == '-')
{
minus = -1;
cstr++;
}
else if (*cstr == '+')
cstr++;

while (*cstr != '\0')
{
if (*cstr > '0' && *cstr < '9')
{
g_nStatus = kValid;
num = num * 10 + (*cstr - '0');
cstr++;
if (((minus>0) && (num > 0x7FFFFFFF)) ||
((minus<0) && (num > 0x80000000)))
{
g_nStatus = kInvalid;
num = 0;
break;
}
}
else
{
g_nStatus = kInvalid;
num = 0;
break;
}
}

if (g_nStatus == kValid)
num = num * minus;

}
return (int)num;
}
};

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