【C语言】关于解决scanf函数调用中的恶意输入/无效输入导致bug问题以及代码实现自动化解决解析

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【C语言】关于解决scanf函数调用中的恶意输入/无效输入导致bug问题以及代码实现自动化解决解析

这里输代码：

#include <stdio.h>

int FormatInput(char opt);

int FormatInput(char opt)
{
	while (1)
	{
		if (opt == 'Y' || opt == 'N')
		{
			if(opt == 'Y')
			{
				return 1;
				break;
			}
			else
			{
				printf("\n\n\n\n\n\n");
				return 0;
				break;
			}
		}
		else
		{
			while(getchar() != 10);// delete meaningless strings
			printf ("\n=============================\n       INVALID DATA ! \n=============================\n");
			printf("Enter valid data (Y or N) to make your choice.\n");
			printf("\nYour choice:");
			scanf("%c",&opt);
		}
	}
}

int main (void)
{
	int num1,num2,num3;
	double average;
	int i,j,k;
	int check;
	char opt;
	
	printf("(Enter any character to start.)");
	
	/* get the input data and provide chances to check and reenter data*/
	do
	{
		i=j=k=0;
		while(i == 0)
		{
		    while(getchar() != 10);
			printf("Enter 1st integer numbers: ");
			i = scanf("%d",&num1);
			while(getchar() != 10);
			if(i == 0) printf ("\n=============================\n       INVALID DATA ! \n=============================\n\n");
			else
			{
				printf("%c",7);// prompt sound rings when enter finished
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\nThe 1st number is %d.\n",num1);
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\n\n\n");
			}
		}
		while(j == 0)
		{
			while(getchar() != 10);
			printf("Enter 2nd integer numbers: ");
			j = scanf("%d",&num2);
			if (j == 0) printf ("\n=============================\n       INVALID DATA ! \n=============================\n\n");
			else
			{
				printf("%c",7);// prompt sound rings when enter finished
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\nThe 2nd number is %d.\n",num2);
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\n\n\n");
			}
		}
		while(k == 0)
		{
			while(getchar() != 10);
			printf("Enter 3rd integer numbers: ");
			k = scanf("%d",&num3);
			if (k == 0) printf ("\n=============================\n       INVALID DATA ! \n=============================\n\n");
			else
			{
				printf("%c",7);// prompt sound rings when enter finished
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\nThe 3rd number is %d.\n",num3);
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\n\n\n");
			}
		}
		while(getchar() != 10);// delete meaningless strings
		//getchar();//delete \n
		printf("%c",7);// prompt sound rings when enter finished
		printf("\n=========== Data has been successfully entered! ===========\n");
		printf("\nThe 1st number is %d.\nThe 2nd number is %d.\nThe 3rd number is %d.\n",num1, num2, num3);
		printf("\n=========== Data has been successfully entered! ===========\n");
		printf("\nAre these numbers what you need?");
		printf("(Y or N)\n");
		printf("\nYour choice:");
		scanf("%c",&opt);
		check=FormatInput(opt);
	}while (check == 0);
	
	printf("\n\n=========== Data enter finished! ===========\n\n");
	printf("%c",7);
	
	/* calculate the average */
	average = (num1 + num2 + num3) / 3.0;
	
	/* display the result */
	printf("\nThe average of %d, %d and %d is %f\n\n",num1, num2, num3, average);
	
	while(getchar() != 10);
	while(getchar() == 10);
	getchar();
	
	return 0;
}

以下是自动化实现的详细解析

• 用户输入时恶意/无意输入除数字外等一切符号：

字母和特殊字符：如果仅仅含有scanf函数输入，字母和特殊字符的额外输入必然导致程序直接退出，于是利用scanf（）也为int函数，其返回值是成功输入的数据的个数的特性，可以先判断scanf("%d",&num1) ==1？，防止输入失败的连带程序自我了结，并利用while(getchar() != 10)消除多余字符。

空格，字母和特殊字符：空格尽管不会导致程序退出，但他们的溢出也会对后面的输入%c和有限的getchar（）造成恶意输入而产生未知的bug，通过**while(getchar() != 10)**配合getchar（）实现完全消除恶意输入，此时不再担心因为在有机可乘的地方乱输入而导致输入Y/N时出现bug——连续执行n次每输入n个非法字符，提供良好的交互式体验
注：getchar（）为int函数，可以返回所输入字符的ASCII码，只要不为10（换行符的ASCII码）就继续getchar（）消除恶意溢出字符

while(i == 0)
		{
		    while(getchar() != 10);
			printf("Enter 1st integer numbers: ");
			i = scanf("%d",&num1);
			while(getchar() != 10);
			if(i == 0) printf ("\n=============================\n       INVALID DATA ! \n=============================\n\n");
			else
			{
				printf("%c",7);// prompt sound rings when enter finished
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\nThe 1st number is %d.\n",num1);
				printf("\n=========== Data has been successfully entered! ===========\n");
				printf("\n\n\n");
			}
		}

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