c - 埃拉托色尼筛程序的分段错误

Question

我正在尝试实现筛算法，它会询问连续数字列表的大小并打印出该列表中的素数，但我遇到了 seg fault: 11 错误。

这是我的代码：

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

#define LIMIT 1000000 /*size of integers array*/

int main(void){
    char n[LIMIT];

    //Reads the size of integer array
    printf("Size of array:\n");
    if((fgets(n, LIMIT, stdin)) == NULL) {
        fprintf(stderr, "Could not read from stdin\n");
        exit(1);
    }

    unsigned long long int i,j;
    int *primes;
    int z = 1;

    primes = malloc(sizeof(n));

    for (i = 2; i < sizeof(n); i++){
    primes[i] = 1; //setting every number in list to 1
    }

    for (i = 2; i < sizeof(n); i++){
        if (primes[i]){
            for (j = i; (i*j) < sizeof(n); j++){
                primes[i * j] = 0; //remove multiples
            }
        } 
    }

    for (i = 2; i < sizeof(n); i++){
        if (primes[i]){
            printf("%dth prime = %llu\n",z++,i);
        }
    }

    free(primes);

    return 0;
}

Answer 1

char n[LIMIT];

使用LIMITbeing的值1000000，这是一个非常大的数组（一百万字节）。这会导致堆栈溢出。您需要为其动态分配内存：

char *n = malloc(LIMIT);

Answer 2

代码n以一种奇怪的方式使用。建议简单地扫描整数n并使用n来结束循环而不是sizeof(n).

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

int main(void){
    unsigned long n;

    //Reads the size of integer array
    buffer[30];
    printf("Size of array:\n");
    if((fgets(buffer, sizeof buffer, stdin)) == NULL) {
        fprintf(stderr, "Could not read from stdin\n");
        exit(1);
    }
    if (sscanf(buffer,"%lu", %n) != 1) {
        fprintf(stderr, "Unable to covert to a number\n");
        exit(1);
    }

    unsigned long i,j;
    int *primes;
    // int z = 1;

    primes = malloc(n * sizeof *primes);

    for (i = 2; i < n; i++){
      primes[i] = 1; //setting every number in list to 1
    }

    for (i = 2; i < n; i++){
        if (primes[i]) {
            for (j = i; (i*j) < n; j++){
                primes[i * j] = 0; //remove multiples
            }
        } 
    }

    for (i = 2; i < n; i++){
        if (primes[i]){
            printf("%dth prime = %llu\n",z++,i);
        }
    }

    free(primes);
    return 0;
}