assert、atexit、bsearch、tolower、offsetof及va_list

最新推荐文章于 2023-02-21 18:43:04 发布

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本文深入探讨了C++编程中的关键概念和技术，包括屏蔽assert函数、使用atexit、二分搜索、大小写转换、结构体偏移量计算以及不定参数函数等。详细解释了每个功能的实现和应用，为读者提供了丰富的实践经验和理论知识。

1.屏蔽assert函数


#define NDEBUG  ("no debug")    //shield the function of assert ... 
#include <assert.h>
#include <stdlib.h>


void
open_record(char *record_name)
{
    assert(record_name!=NULL);
        /* Rest of code */
    printf("\nRecord name is:%s\n", record_name);
}

int
main(void)
{
      open_record(NULL);
      open_record("I love janesnf...");
      open_record(NULL);

      return 0;
}

2. 调用atexit

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

void
test_atexit0(void)
{
    printf("\nHosfore 000000 is using atexit function ...\n");
}

void
test_atexit(void)
{
    printf("\nHosfore is using atexit function ...\n");
}

int
main()
{
    int i = 0;
    atexit(test_atexit);
    atexit(test_atexit0);
    atexit(test_atexit);
    atexit(test_atexit0);

    for (; i < 100; i++)
        printf("\n----\n");

    return 0;
}

3.调用二分搜索函数，搜索从数组的平均值开始

#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#define  DEBUG 0

int
compare(const void *key, const void *current)
{
    assert(key != NULL);
    assert(current != NULL);

#if(DEBUG)
    printf("\nIn %s and key val:%d, current val:%d\n",\
            __func__, *(int*)key, *(int*)current);
#endif

    if (*(int*)key > *(int*)current)
        return 1;
    else if (*(int*)key == *(int*)current)
        return 0;
    else
        return -1;
}

int
main()
{
    int key = 2, arr[10], i = 0, *rt;
    for (; i < 10; i++)
       arr[i] = 2+i;
#if(DEBUG)
    printf("\nIn %s and sizeof arr is:%d, sizeof int is:%d\n",\
             __func__, sizeof(arr)/sizeof(arr[0]), sizeof(int));
#endif
    rt = bsearch(&key, arr, sizeof(arr)/sizeof(arr[0]), sizeof(int), compare);
    if (rt)
        printf("\nbsearch result of key:%d  is:%d and memory addr is:%p\n",\
                key, *rt, rt);
    return 0;
}

4.大小写字母转换函数调用

#include<ctype.h>
#include<stdio.h>
#include<string.h>

int main(void)
{
    int loop;
    char string[]="THIS IS A TEST";

    printf("Orig: %s\n",string);
    for(loop=0;loop<strlen(string);loop++)
        string[loop]=tolower(string[loop]);
    printf("Tolowered:  %s\n",string);
    return 0;
}

5.求结构体属性在其内部地址偏移函数offsetof

#include<stddef.h>
#include<stdio.h>

int main(void)
{
    struct user{
        char name[50];
        char alias[50];
        int level;
    };

    printf("level is the %d byte in the user structure.\n",
             offsetof(struct user,level));
}

6.支持不定参数个数的函数（源自网络）

#include<stdarg.h>
#include<stdio.h>

void
sum(char *, int, ...);

int
main(void)
{
    sum("The sum of 10+15+13 is %d.\n",3,10,15,13);
    return 0;
}

void
sum(char *string, int num_args, ...)
{
    int sum=0;
    va_list ap;
    int loop;

    va_start(ap,num_args);
    for(loop=0;loop<num_args;loop++)
        sum+=va_arg(ap,int);

    printf(string,sum);
    va_end(ap);
}