c-为什么在函数search_lastname中出现分段错误

Question

以下程序接受来自用户的学生姓名、姓氏和分数数据。函数search_lastname应该搜索给定姓氏的记录。但它给分割带来了缺陷。另一个功能是打印记录，并且已经为尚未添加到程序中的其他功能创建了切换用例。

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
char **first_name, **last_name;
float *score;
int entry;
void print();
void search_lastname(char search_last_name[21]);
int main()
{
int i,option;
char search_last_name[21];
do
{
printf("nPlease indicate the number of records you want to enter (The minimum number of entries is 5) :");                     
scanf("%d",&entry);
}
while(entry<=4);
score=(float*)malloc(entry*sizeof(float));
first_name=(char**)malloc(entry*sizeof(char*));
last_name=(char**)malloc(entry*sizeof(char*));
for(i=0;i<entry;i++)
{
first_name[i]=(char*)malloc(21*sizeof(char));
last_name[i]=(char*)malloc(21*sizeof(char));
}
printf("Please input records of students (enter a new line after each record), with following format first name last name score n");
for(i=0;i<entry;i++)
{
scanf("%s%s%f",&first_name[i],&last_name[i],&score[i]);                                                             /*Input of records itself*/
}
do
{
printf("nPlease choose the appropriate options :");                                                /*Switch statement for choosing options.*/
printf("nPrint records (press 1)nAdd a new record (press 2)nDelete records (press 3)nSearch by last name (press 4)nSort by score (press 5)nSort by last name (press 6)nFind Median score (press 7)nExit the Program (press 0)");
scanf("%d",&option);
switch(option)
{
case 1  :print();
break;
case 2  :
break;
case 3  :
break;
case 4  :
printf("n Please enter the last name you want to search: ");
scanf("%s",search_last_name);
search_lastname(search_last_name);
break;
case 5  :
break;
case 6  :
break;
case 7  :
break;
case 0  :
break;
default : 
printf("n Please enter a valid option.");
}
}
while(option>=1 && option<=7);
return 0;
}
void print()
{
int i;
printf("n The records of students are as follows :");
for(i=0;i<entry;i++)
{
printf("nFirst name:%s, Last name:%s, Score:%fn",&first_name[i],&last_name[i],score[i]);
}
}

void search_lastname(char search_last_name[21])                                     /*Funtion to search by last name*/  
{
int i,counter=0;
for(i=0;i<entry;i++)
{
if(strcmp(search_last_name,last_name[i])==0)
{
printf("nFirst name:%s, Last name:%s, Score:%fn",first_name[i],last_name[i],score[i]);
}
}
}

Answer 1

您的问题在于scanf()函数的使用。您需要更改

scanf("%s%s%f",&first_name[i],&last_name[i],&score[i]);

至

scanf("%20s %20s %f", first_name[i], last_name[i], &score[i]);

如果没有长度修饰符，%s说明符将无法分隔输入的字符串，因此将重写超过分配内存的内存区域，从而导致未定义的行为。

此外，强烈建议您检查scanf()的返回值，以确保输入正确。

注：

1. main()的推荐签名是int main(void)
2. 不要强制转换malloc()和族的返回值