#include 
     
      #include 
      
       #include 
       
        int my_atoi(char *str){    if(NULL == str)    {        printf("argc is null\n");        return -1;            }    while(' ' == *str)        str++;    int flag = 1;    if('-' == *str)    {        flag = -1;        str++;    }    if('+' == *str)    {        str++;    }    unsigned int sum = 0;    while(*str)    {        if(*str >= '0' && *str <= '9')        {            int tmp = *str - '0';            sum *= 10;            sum += tmp;            //此处判断溢出的目的是避免sum在计算过程中溢出             if((1 == flag) && (sum > INT_MAX))            {                printf("int  正数溢出\n");                return -1;            }            //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 + 1;            if((-1 == flag) && (sum > absIntMin))            {                printf("int 负数溢出\n");                return -1;            }        }        else        {            printf("str (%s) exists illegal character\n", str);            return -1;        }        str++;    }    return flag * sum;}
       
      
     

测试代码

#include 
     
      #include 
      
       extern int my_atoi(char *str);int main(int argc, char *argv[]){    char a[20] = {
   '\0'};    while(1)    {        scanf("%s", a);        printf("count = %d\n", my_atoi(a));    }    return 0;}