[C++知识库]6.18.5-PointersOnC-20220131

因为没注意到'三目操作符'优先级比'+'低，漏了一个括号，造成内存越界，调试还看不出来，幸好有printf大法。

#include<stdio.h>
#include<stdlib.h>
#include<limits.h>
//#include<time.h>
void Initialize_bit(char *arr,int n);
void Clear_bit(char *arr,int n);
int Test_bit(char *arr,int n);
int main(){
	//srand((unsigned int)time(0)*10000);
	int number_max=0;
	int count_prime_number=0;
	//for(;number_max<9999;number_max=rand()%INT_MAX);
	number_max=1000;
	printf("number_max=%d\n",number_max);
	int *numbers=(int *)calloc(number_max+1,sizeof(int));
	char *numbers_tag=(char *)calloc((number_max+1)/CHAR_BIT+((number_max+1)%CHAR_BIT?1:0),sizeof(char));
	for(int i=0;i<number_max+1;*(numbers+i)=i,i++);
	Initialize_bit(numbers_tag,(number_max+1)/CHAR_BIT+((number_max+1)%CHAR_BIT?1:0));//记得加括号,因为'三目操作符'优先级比'+'低
	Clear_bit(numbers_tag,0);
	Clear_bit(numbers_tag,1);
	for(int j=2,flag=0;1;j++,flag=0){
		if(j!=2&&!(j%2))
			j++;
		for(int i=j*2;i<number_max+1;i+=j)
			if(Test_bit(numbers_tag,i)){
				Clear_bit(numbers_tag,i);
				flag=1;
			}
		if(!flag)
			break;
	}
	for(int i=1;i<number_max+1;count_prime_number+=Test_bit(numbers_tag,i)?1:0,i++);
	printf("There were %d prime number between 0-%d:\n",count_prime_number,number_max);
	for(int i=0,count=0;i<number_max+1;i++){
		if(Test_bit(numbers_tag,i)){
			count++;
			printf("%d%c",*(numbers+i),count%10?32:10);
		}
	}
	free(numbers);
	numbers=NULL;
	free(numbers_tag);
	numbers_tag=NULL;
return 0;}
//
void Initialize_bit(char *arr,int n){
	for(int i=0;i<n;*(arr+i)|=0xff,i++);
}

void Clear_bit(char *arr,int n){
	*(arr+n/CHAR_BIT)&=~(1<<n%CHAR_BIT);
}

int Test_bit(char *arr,int n){
	return *(arr+n/CHAR_BIT)>>n%CHAR_BIT&1;
}