c - 带有数组的段错误(核心转储)C 程序

Question

#include <stdio.h>
#include <string.h>
#define SIZE 1000

int main(void)
{
char sent[] = "\0";        
char alpha[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz ";
unsigned int count;
unsigned int k;
unsigned int j;                                                            

printf("Please enter a sentence to analyze\n");
fgets(sent, SIZE, stdin);  


printf("\n     Letter\t ||\tAmount\n");
printf(" ================================\n");

    for(j = 0; alpha[j] != '\0'; j++)
    {
        count = 0;

        for (k = 0; sent[k]!= '\0'; k++)
        {

            if ( alpha[j] == sent[k])
            {                          
                count++;                                   
            }

        }

        printf("\t%c\t ||\t %u\n", alpha[j], count);
        printf(" --------------------------------\n");  
    }  


    return 0;

}

每次运行此程序时，我都会收到错误“段错误(核心转储)”。不过程序似乎运行正确。为什么会发生这种情况？我可以采取什么措施来解决这个问题？

Answer 1

在您的代码中，

 char sent[] = "\0"; 

分配的数组大小仅等于所提供的初始值设定项“\0”(和空终止符)的大小。所以，稍后，通过这样做

fgets(sent, SIZE, stdin);

您正在访问超出范围的内存。这会调用 undefined behavior .

引用 C11 标准，第 §6.7.9 章

If an array of unknown size is initialized, its size is determined by the largest indexed element with an explicit initializer. [...]

您需要的是在定义时提供数组大小，例如

 char sent[SIZE] = "\0";