如何处理用户输入错误

Question

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

struct vector
{
    double x;
    double y;
    double z;
};

struct vector *array;
double length(struct vector*);

int main()
{
    int num,i;
    double xin;
    double yin;
    double zin;
    char buffer[30];
    char buffer2[30];

    printf("Enter number of vectors:");
    fgets(buffer, 30, stdin);
    sscanf(buffer, "%d", &num);

    array = malloc( sizeof(struct vector) * num);

    for(i=0;i<=num;i++)
    {
        printf("Please enter x y z for the vector:");
        fgets(buffer2,100,stdin);
        sscanf(buffer2, " %lf %lf %lf", &xin, &yin, &zin);

            array[i].x = xin;
            array[i].y = yin;
            array[i].z = zin;
    }

    for(i=0;i<=num;i++)
    {
        printf( "Vector:%lf %lf %lf has a length of %lf\n", array[i].x, array[i].y, array[i].z, length(&array[i]));
    }
}


double length(struct vector* vec)
{
    return sqrt( (vec->x * vec->x) + (vec->y * vec->y) + (vec->z * vec->z) );
}

好的，上面的代码差不多完成了，它询问用户向量的数量，然后它询问用户这些向量的值，然后它会计算长度并相应地打印出来。

我试图在这里检查一些错误，但我似乎无法得到它...我查找了 fgets 和 sscanf 的所有可能返回值，但我似乎无法得到它

防御功能

FIRST printf-----input 只能是大于 0 的单个数字，EOF 应该返回类似 printf("enter a number--bye!") 的消息，所以我尝试了

while( sscanf(buffer, "%d", &num) ==1 && num > 0 )

但如果输入 3dadswerudsad 之类的内容，它仍然有效

此外，当用户输入向量的 3 个值时，如果为向量输入了除 3 个双精度之外的任何值，则程序应该以一条消息终止，所以我尝试了

while( sscanf(buffer2, "%lf %lf %lf", &xin, &yin, &zin) ==3 )

但它不会检查这些不正确的输入！！

我要疯了

Answer 1

以下代码：

• 编译干净
• 显示了几个错误检查示例

发布的代码引发了编译器警告，即在没有返回语句的情况下到达非 void 函数的末尾（需要更正警告）。
要查看所有警告，请在为gcc 编译时启用所有警告，使用参数：-Wall -Wextra -Wpedantic

顺便说一句：正确声明结构的荣誉

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

struct vector
{
    double x;
    double y;
    double z;
};

struct vector *array;

// prototypes
double length(struct vector*);

int main()
{
    int num,i;
    double xin;
    double yin;
    double zin;
    char buffer[30];
    char buffer2[30];

    printf("Enter number of vectors:");
    if( NULL == fgets(buffer, 30, stdin) )
    { // then fgets failed
        perror( "fgets for num vectors failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, fgets successful

    if( 1 != sscanf(buffer, " %d", &num) )
    { // then sscanf failed
        perror( "sscanf for num Vectors failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, sscanf failed


    // add validation of num here


    if( NULL == (array = malloc( sizeof(struct vector) * num) ))
    { // then, malloc failed
        perror( "malloc for num Vectors failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, malloc successful


    for(i=0;i<=num;i++)
    {
        printf("Please enter x y z for the vector:");
        if( NULL == fgets(buffer2,100,stdin) )
        { // then fgets failed
            perror( "fgets for vector values failed" );
            free(array); // cleanup
            exit( EXIT_FAILURE );
        }

        // implied else, fgets successful

        if( 3 != sscanf(buffer2, " %lf %lf %lf", &xin, &yin, &zin) )
        { // then sscanf failed
            perror( "sscanf for vector values failed" );
           free(array); // cleanup
            exit( EXIT_FAILURE );
        }

        // implied else, sscanf successful

        array[i].x = xin;
        array[i].y = yin;
        array[i].z = zin;
    } // end for

    for(i=0;i<=num;i++)
    {
        printf( "Vector:%lf %lf %lf has a length of %lf\n",
                array[i].x,
                array[i].y,
                array[i].z,
                length(&array[i]));
    } // end for

    free(array); // cleanup

    return(0);
} // end function: main