我需要使用指针来代码。没有数组，没有结构。例如，如果我需要一个浮点数组来保存分数，请不要使用浮点数[15]。而是使用float *得分，然后使用动态内存分配来保存所需的内存。我必须最佳地使用内存，即如果你只有6个分数，我需要用来指向sizeof（float）* 6个字节的内存块。同样，要保存名称，而不是使用2D char数组，请使用2D指针（char firstName [15] [20]→char ** firstName）。
我有下面的C代码，我需要使用2d指针的帮助。代码编译并运行，但在我输入名称后如果崩溃并且在工作之后这么长时间我就卡住了。
提前谢谢
#include <stdio.h>
#include<string.h>
#include<stdlib.h>
#include<time.h>
void Option_Scren();
void print_records(int size, char **firstname, char **lastname, float *score);
void search_by_firstname(int size, char **firstname, char **lastname, float *score);
void search_by_lastname(int size, char **firstname, char **lastname, float *score);
void sort_by_score(int size, char **firstname, char **lastname, float *score);
void sort_by_lastname(int size, char **firstname, char **lastname, float *score);
int main(void)
{
char **First_Name;
char **Last_Name;
float *Score_;
int n = 0;
int i = 0;
int x = -1;
First_Name = (char **)malloc(sizeof(char *));
Last_Name = (char **)malloc(sizeof(char *));
Score_ = (float *)malloc(sizeof(int)*15);
for(i=0; i<15; i++)
{
First_Name[i] = (char *)malloc(20*sizeof(char));
Last_Name[i] = (char *)malloc(20*sizeof(char));
}
//char *nametofind = (char *)malloc(20*sizeof(char));
printf("Please indicate the number of records you want to enter (min 5, max 15):\n");
scanf("%d", &n);
printf("Please input records of students (enter a new line after each record), with the following format \nFirstname Lastname Score\n");
for (i = 0; i<n; i++)
{
scanf("%s %s %f", &First_Name[i][0], &Last_Name[i][0], &Score_[i]);
}
do
{
printf("\n---you may access the records by---\n");
printf("Print records (press 1)\n");
printf("Search by first name (press 2)\n");
printf("Search by last name (press 3)\n");
printf("Sort by score (press 4)\n");
printf("Sort by last name (press 5)\n");
printf("Exit program (press 0)\n");
printf("--------------------------\n\n");
printf("Please a function by entering a value from 0 to 5.\n");
scanf("%d", &x);
printf("You have selected option: %d\n", x);
switch (x)
{
case 1:
print_records(n, First_Name, Last_Name, Score_);
break;
case 2:
search_by_firstname(n, First_Name, Last_Name, Score_);
break;
case 3:
search_by_lastname(n, First_Name, Last_Name, Score_);
break;
case 4:
sort_by_score(n, First_Name, Last_Name, Score_);
break;
case 5:
sort_by_lastname(n, First_Name, Last_Name, Score_);
break;
default: printf("Please only enter a number from 0 to 5\n");
}
}
while (x != 0);
printf("Thank You \nGood Bye\n");
return 0;
}
void print_records(int size, char **firstname, char **lastname, float *score)
{
int i = 0;
for (i = 0; i < size; i++)
{
printf("First Name: %s, Last Name: %s, Score: %.2f\n", firstname[i], lastname[i], score[i]);
}
}
void search_by_firstname(int size, char **firstname, char **lastname, float *score)
{
int i = 0;
char *Name_Search = (char *)malloc(20*sizeof(char));
printf("Please enter the first name of student record you wish to print: ");
fgets(Name_Search, 20, stdin);
for (i = 0; i<size; i++)
{
if (strcmp(Name_Search, firstname[i]) == 0)
{
printf("First Name: %s, Last Name: %s, Score: %.2f\n", firstname[i], lastname[i], score[i]);
}
}
}
void search_by_lastname(int size, char **firstname, char **lastname, float *score)
{
int i = 0;
char *Name_Search = (char *)malloc(20*sizeof(char));
printf("Please enter last name of student record you wish to print: ");
fgets(Name_Search, 20, stdin);
for (i = 0; i<size; i++)
{
if (strcmp(Name_Search, lastname[i]) == 0)
{
printf("First Name: %s, Last Name: %s, Score: %.2f\n", firstname[i], lastname[i], score[i]);
}
}
}
void sort_by_score(int size, char **firstname, char **lastname, float *score)
{
int i = 0;
int j = 0;
float tempscore;
char tempfirstname[20];
char templastname[20];
// bubble sort
for (i = 0; i<size - 1; i++)
{
for (j = 0; j<size - i - 1; j++)
{
if (score[j]>score[j + 1])
{
tempscore = score[j];
score[j] = score[j + 1];
score[j + 1] = tempscore;
strcpy(tempfirstname, firstname[j]);
strcpy(firstname[j], firstname[j + 1]);
strcpy(firstname[j + 1], tempfirstname);
strcpy(templastname, lastname[j]);
strcpy(lastname[j], lastname[j + 1]);
strcpy(lastname[j + 1], templastname);
}
}
}
print_records(size, firstname, lastname, score);
}
void sort_by_lastname(int size, char **firstname, char **lastname, float *score)
{
int i = 0;
int j = 0;
float tempscore;
char tempfirstname[20];
char templastname[20];
// bubble sort
for (i = 0; i<size - 1; i++)
{
for (j = 0; j<size - i - 1; j++)
{
if (strcmp(lastname[j], lastname[j + 1])>0)
{
strcpy(tempfirstname, firstname[j]);
strcpy(firstname[j], firstname[j + 1]);
strcpy(firstname[j + 1], tempfirstname);
strcpy(templastname, lastname[j]);
strcpy(lastname[j], lastname[j + 1]);
strcpy(lastname[j + 1], templastname);
tempscore = score[j];
score[j] = score[j + 1];
score[j + 1] = tempscore;
}
}
}
print_records(size, firstname, lastname, score);
}
答案 0 :(得分：1)
基本上你正在做的是为一些数据使用动态分配存储，你分配的方式有一些问题，见下文。此外，不要投放malloc的返回值，void*与标准C中的其他指针兼容。其次，您不需要执行sizeof(char)，它是＆＃39 ; s在标准中被定义为1。
// suppose the number of elements you want to store if 15
#define N 15
char **First_Name;
char **Last_Name;
float *Score_;
// First_Name = (char **)malloc(sizeof(char *));
// you are allocating an buffer to hold ONE char* here, use following instead
First_Name = malloc(N * sizeof(char*));
// Last_Name = (char **)malloc(sizeof(char *));
// same issue here, should be:
Last_Name = malloc(N * sizeof(char*));
// Score_ = (float *)malloc(sizeof(int)*15);
// Score_ is an pointer of floats, so you cannot use sizeof(int) to calculate the size
Score_ = malloc(N * sizeof(float));
for(i=0; i<N; i++) {
First_Name[i] = malloc(20);
Last_Name[i] = malloc(20);
}