面试常见题 _0227

1.#将一个int型数据的第三位置1，再将其第三位清零，其它位不变
#include

#define BIT3_1 0x08
#define BIT3_0 0xfffffff7

int main(int argc, const char *argv[])
{
    int a=0xffffff00;

    a=a|BIT3_1;
    printf("%#x\n",a);
    a=a&BIT3_0;
    printf("%#x\n",a);
    return 0;
}
2.#用malloc分配0个空间，malloc的返回值是一个地址，不是NULL
#include

int main(int argc, const char *argv[])
{
    char *ptr, *ptr1 ;
    ptr1 = (char *)malloc(0);
    if((ptr=(char *)malloc(0)) == NULL)
        printf("Got a null pointer\n");
    else
    {
        printf("Got a valid pointer\n");
        printf("%p\n",ptr);
        printf("%p\n",ptr1);
        free(ptr);
        free(ptr1);
    }
    return 0;
}
3.#运算符优先级的应用
#include

int main(int argc, const char *argv[])
{
    int a = 5, b = 7, c;
    c = a+++b;
    printf("a=%d\n",a);
    printf("b=%d\n",b);
    printf("c=%d\n",c);
    
    return 0;
}
4.#运算符优先级的应用
#include

int main(int argc, const char *argv[])
{
    int a = 2, b ;
    b = a<<2+3;
    printf("c=%d\n",b);
    return 0;
}
5.#变量的存活期
#include
#include
#include

void GetMemory(char *p)
{
    p = (char *)malloc(100);
}

int main(int argc, const char *argv[])
{
    char *str = NULL;
    GetMemory(str);
    strcpy(str,"hello world");
    printf("str=%s\n",str);
    return 0;
}