C - 在代码中引用时的 argc 位置问题

Question

我遇到的问题是，如果命令行提供的参数不足，我希望程序请求所有值。出于某种原因，当我提供 2 个参数中的 3 个时，它会起作用，但如果提供 1 个参数或没有提供任何参数，我希望它能工作。

我的代码

    #include <stdio.h>
    #include <stdlib.h>
    #include <math.h>
    float areaOfcircle(float radius_circle)
    {
        float area_circle;
        area_circle = M_PI * radius_circle * radius_circle;
        return area_circle;
    }
    void resitance_current(float length, float area_circle, float voltage, float* resistance, float* current)
    {
        float resistivity;
        resistivity = 1.782*pow(10, -8);
        *resistance = ((resistivity*length) / area_circle);
        *current = (voltage / *resistance);
    }
    void radius_check(float radius)
    {
        if (radius <= 0)
        {
            printf("Radius cant be less than or equal to 0");
            exit(1);
        }
    }
    void voltage_check(float voltage)
    {
        if (voltage <= 0)
        {
            printf("Voltage cant be less than or equal to 0");
            exit(1);
        }
    }
    void length_check(float length)
    {
        if (length <= 0)
        {
            printf("Length cant be less than or equal to 0");
            exit(1);
        }
    }
    void validation(float radius, float voltage, float length)
{
    radius_check(radius);
    voltage_check(voltage);
    length_check(length);
}
    int main(int argc, char *argv[])
    {
        float radius, voltage, length, current, resistance;
        float length_u, length_l;
        //dumpargs(argc, argv);
        radius = atof(argv[1]);
        voltage = atof(argv[2]);
        length = atof(argv[3]);
        if (argc != 4)
        {
            printf("Not enough arguments suppliedn");
            printf("Enter the radius of wire : ");
            scanf("%f", &radius);
            radius_check(radius);
            printf("Enter the Voltage of circuit : ");
            scanf("%f", &voltage);
            voltage_check(voltage);
            printf("Enter the Length of Wire : ");
            scanf("%f", &length);
            length_check(length);
        }
        validation(radius, voltage, length);
        resitance_current(length, areaOfcircle(radius), voltage, &resistance, &current);
        printf("Resistance = %f , Current = %fn", resistance, current);
        printf("nEnter the Upper Length of Wire : ");
        scanf("%f", &length_u);
        printf("nEnter the Lower Length of Wire : ");
        scanf("%f", &length_l);
        if ((length_l < 0) || (length_l >= length_u))
        {
            printf("nImpossible for Lower Length < 0 or to be larger then Length Upper");
            exit(1);
        }
        else
        {
            for(length_l = length_l; length_l<=length_u; length_l++)
            {
                resitance_current(length, areaOfcircle(radius), voltage, &resistance, &current);
                printf("nLength = %0.3f Resistance = %0.3f , Current = %0.3f", length, resistance, current);
                length = (length_l + 1);
            }
        }
        return 0;
    }

正如你从代码"if （argc ！= 4）"中看到的，如果值是通过命令行提供的，则会再次请求并重写这些值。 我试图找到对此的评价，因此，如果程序本身是从CMD运行的，则将请求值，但如果提供了所有值，则代码将正常工作。除了 argc iss 之外，代码还按要求进行操作。

提前感谢您的任何帮助

Answer 1

如果传递的参数小于 4 ，则越界访问。

只需修改代码，如下所示。那就是首先检查传递的参数数量，然后访问argv。

    if (argc != 4) // or if (argc < 4)
    {
        printf("Not enough arguments suppliedn");
        printf("Enter the radius of wire : ");
        scanf("%f", &radius);
        printf("Enter the Voltage of circuit : ");
        scanf("%f", &voltage);
        printf("Enter the Length of Wire : ");
        scanf("%f", &length);
    }
    else {
        radius = atof(argv[1]);
        voltage = atof(argv[2]);
        length = atof(argv[3]);
    }
    radius_check(radius);
    voltage_check(voltage);
    length_check(length);

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还需要检查scanf的返回值，阅读这个关于如何检查scanf返回值。