带数组的段错误（核心转储）C 程序

Question

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

int main(void)
{
char sent[] = "[=10=]";        
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] != '[=10=]'; j++)
    {
        count = 0;

        for (k = 0; sent[k]!= '[=10=]'; k++)
        {

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

        }

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


    return 0;

}

每次我运行这个程序我都会得到错误 "Segmentation Fault (Core Dumped)"。但是该程序似乎运行正确。为什么会发生这种情况，我该怎么做才能解决这个问题？

Answer 1

在您的代码中，

 char sent[] = "[=10=]";

分配的数组大小仅等于提供的初始值设定项 "[=13=]"（和空终止符）的大小。所以，稍后，通过做

fgets(sent, SIZE, stdin);

您正在访问超出限制的内存。这会调用 undefined behavior.

引用C11标准，章节§6.7.9

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

您需要在定义时提供数组大小，如

 char sent[SIZE] = "[=12=]";

带数组的段错误（核心转储）C 程序

Segmentation Fault (Core Dumped) C Program with Arrays

c

arrays

string

fgets