c语言 将字符串转化为整数

/*
将数字字符串，转换成整数输出
例：“1234”输出 1234
*/

#include<stdio.h>

int str_validity = 0;
int charnum_to_int(char *str)
{
int num = 0, i = 0;
if (str == NULL)
{
str_validity = 1;
return 0;
}
if (*str == '-' || *str == '+')
{
i = '*str';
while (*(++str))
{
int num1;
if (*str >= 48 && *str <= 57)
{
if (*str == '0'&&num == 0)
continue;
else
num = num * 10 + (*str - 48);
num1 = num;
if ((num1&(1 << 31)) < 0)
str_validity = 1;
}
else
{
str_validity = 1;
break;
}

}
if (i == '-')
return num*-1;
else
return num;
}
while (*str)
{
int num1;
if (*str >= 48 && *str <= 57)
{
if (*str == '0'&&num == 0)
continue;
else
num = num * 10 + (*str - 48);
num1 = num;
if ((num1&(1 << 31) )< 0)
{
str_validity = 1;
break;
}
}
else
{
str_validity = 1;
break;
}
str++;
}
return num;
}

int main()
{
char *str = "-02147483647";//2 ^32
int num = 0;
num=charnum_to_int(str);
if (str_validity == 0)
printf("%d\n", num);
else
printf("该字符串不合法\n");
return 0;
}