归零后的段错误

Question

我们在这学期学习了使用 C 进行编程，在我们的第一个作业中，我们被要求使用手册和库实现打印 sin(x)、cos(x) 和 tan(x) 的值列表。所以，我写了下面的代码：

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

#define START   0
#define STOP    360
#define STEP    10

#define PI      3.14159265358979323846  /*For conversion: degrees <-> radians */

double rad(double x);   /* Converts angle in degrees to radians */
double next_term(double angle, int term_index);

/* Function prototypes for manual implementation of sin(x), cos(x) and tan(x) */
double sin_series(double x);
double cos_series(double x);
double tan_series(double x);


int main() {

    /* Creating and printing the table title:
    ** ==================================================================== */

    char table_title[] = "   n | ";
    strcat(table_title, "sin series | sin library | ");
    strcat(table_title, "cos series | cos library | ");
    strcat(table_title, "tan series | tan library | ");

    printf("%s \n", table_title);

    /* ==================================================================== */



    /* Creating and printing the line between the title and the table:
    ** ==================================================================== */

    char* second_line = (char*)malloc((strlen(table_title) + 1) * sizeof(char));

    for (int i = 0; i < strlen(table_title) - 1; i++) {
        second_line[i] = '=';
    }

    second_line[strlen(table_title)] = '[=10=]';

    printf("%s \n", second_line);

    /* ==================================================================== */

    free(second_line);

    /* Creating each line of the table and printing it:
    ** ==================================================================== */

    for (int angle = 0; angle < 360; angle += 10) {

        printf("%4i | ", angle);
        printf("%10.5f | %11.5f | ",sin_series(angle), sin(rad(angle)) );
        printf("%10.5f | %11.5f | ",cos_series(angle), cos(rad(angle)) );
        printf("%10.5f | %11.5f | ",tan_series(angle), tan(rad(angle)) );
        printf("\n");
    }

    return 0;   
}

double rad(double x) {
    return ((PI * x) / 180);
}

double next_series_term(double angle, int term_index) {
    double result = 1.0;

    for (int i = 0; i < term_index; i++) {
        result *= angle;
        result /= (i + 1);
    }

    return result;
}

unsigned long long factorial(int x) {

    unsigned long long result = 1;

    for (int i = 0; i < x; i++) {
        result *= (i + 1);
    }

    return result;
}

double sin_series(double x) {

    double result = 0;

    if (x == 0 || x == 180 || x == 360) {
        result = 0;
    }
    else {
        for (int i = 0; i < 100; i++) {

        /* Calculating the next term to add to result to increase precision.*/

        double next_term = next_series_term(rad(x), 2*i + 1);
        next_term *= pow(-1,i);


        result += next_term; 
        }
    }


    return result;  
}

double cos_series(double x) {

    double result = 0;

    if (x == 90 || x == 270) {
        result = 0;
    }
    else {
        for (int i = 0; i < 100; i++) {

        /* Calculating the next term to add to result to increase precision.*/

        double next_term = next_series_term(rad(x), 2*i);
        next_term *= pow(-1,i);     

        result += next_term; 
        }

    }

    return result;  
}

double tan_series(double x) {
        return sin_series(x)/cos_series(x); //non-portable! searching for
                                            // better solution
}

但是这段代码在返回 0 后导致分段错误，正如我在使用 gdb 后发现的那样，这让我完全困惑。作为 C 和编程的新手，这完全让我感到困惑。请帮忙。

Answer 1

这个声明

char table_title[] = "   n | ";

声明 table_title 为 8 个字符的数组。当您将其他字符串追加到数组的末尾时，您将越界并具有 undefined behavior.

要么指定一个足够大的大小来容纳您需要的所有数据，要么使用完整的字符串正确初始化它。

Answer 2

table_title 您分配了一个字符串，因此 sizof(table_title) 将无法保存您传递的整个字符串，因此越界访问数组是未定义的行为，可能会导致崩溃。

Answer 3

为什么使用 table_title？没有必要。只需使用 printf.

printf ("sin series | sin library | cos series | cos library | tan series | tan library | ");

您已静态声明 table_title。 free() 用于释放动态分配的内存。那就去做吧。不会出现分段错误。

Answer 4

好的，那么你可以使用 printf as

printf (
    "sin series | sin library | " \
    "cos series | cos library | " \
    "tan series | tan library | ");

没有换行。试试这个。 :)

归零后的段错误

Segmentation fault after returning zero

c

segmentation-fault