原创：实现atoi函数

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

int my_atoi(char *str)
{
    if(NULL == str)
    {
        printf("argc is null\n");
        return -;
    }
    while(' ' == *str)
        str++;
    int flag = ;
    if('-' == *str)
    {
        flag = -;
        str++;
    }
    if('+' == *str)
    {
        str++;
    }
    unsigned int sum = ;
    while(*str)
    {
        if(*str >= '' && *str <= '')
        {
            int tmp = *str - '';
            sum *= ;
            sum += tmp;
            //此处判断溢出的目的是避免sum在计算过程中溢出
            if(( == flag) && (sum > INT_MAX))
            {
                printf("int  正数溢出\n");
                return -;
            }
            //计算最小int的绝对值，注意要使用unsigned int否则会溢出
            unsigned int  absIntMin = (unsigned int)INT_MAX + ;
            if((- == flag) && (sum > absIntMin))
            {
                printf("int 负数溢出\n");
                return -;
            }
        }
        else
        {
            printf("str (%s) exists illegal character\n", str);
            return -;
        }
        str++;
    }
    return flag * sum;
}

测试代码

#include <float.h>
#include <limits.h>
extern int my_atoi(char *str);
int main(int argc, char *argv[])
{
    char a[] = {'\0'};
    while()
    {
        scanf("%s", a);
        printf("count = %d\n", my_atoi(a));
    }
    return ;
}