显示结构

Question

该程序旨在根据用户的输入显示视频游戏库存。用户需要使用 num_of_games 确定循环运行多长时间。我们必须使用切换循环来确定类型。它可以编译，但无法正确显示。

#include <stdio.h>
#include <string.h>
#define MAX 16

typedef enum genre_type{ action = 0, rpg = 1, simulation = 2, 
                        strategy = 3, sports = 4} genre_t;

typedef struct{
    char title[MAX];
    int num_sold;
    genre_t genre;
}game_s;
// suppose to use functions and enum list for determining the genre
void get_game_info(game_s *ptr);
void display_inventory(game_s game[], int num_of_games);


int
main(void){

    int i=0, num_of_games;
    int c_game=0;
    game_s game[num_of_games];

    printf("How many games are there in inventory? ");
    scanf("%d", &num_of_games);
    fflush(stdin);
    printf("\n");
    while(c_game < num_of_games){
        printf("\n");
        get_game_info(&game[c_game]);
        c_game++;
    }
    printf("\n");
    display_inventory(game, num_of_games);


    return(0);
}
void get_game_info(game_s *ptr)
{       
        int i, str_len, genre, num_sold;

        printf("Title of game <maximum of 15 characters>: ");
        gets(ptr->title);
        str_len = strlen(ptr->title);
            if(str_len >= 15){
                printf("Title will be truncated\n");
                ptr->title[MAX]= '\0';
            }
        printf("Number sold: ");
        scanf("%d", &ptr->num_sold);
        fflush(stdin);
        printf("Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): ");
        scanf("%d", &ptr->genre);
        fflush(stdin);
            if(ptr->genre>4){
                printf("Not a valid genre");
        fflush(stdin);  
}
}
void display_inventory(game_s game[], int num_of_games)
{   
    int i, genre;

    printf("Title\t\t\t\t\t\tQuantity Sold\t\t\t\t\t\tGenre");
    printf("\n=====\t\t\t\t\t\t=============\t\t\t\t\t\t=====\n");
    for(i=0; i < num_of_games; i++){
    switch(genre){
        case action: printf("Action"); break;
        case rpg: printf("RPG"); break;
        case simulation: printf("Simulation"); break;
        case strategy: printf("Strategy"); break;
        case sports: printf("Sports"); break;
        default: puts("Not a choice. Try again"); break;

我认为这是导致大部分问题的原因。我不知道我是否在 game[I].title 和其他人中调用了该结构。 问题出在我认为的结构调用上。如果我使用 game_s[I].title 我得到“预期的表达式之前”错误，如果我使用 game[I].title 它不能正确打印

    printf("%s\t\t\t\t\t\t%d\t\t\t\t\t\t%s", game[i].title, game[i].num_sold, game[i].genre);
    printf("\n");
    }
    }
}

Answer 1

我认为问题出在game_s game[num_of_games];，因为num_of_games 没有启动。

应该是：

printf("How many games are there in inventory? ");
scanf("%d", &num_of_games);
game_s * game_s game = (game_s *) malloc(num_of_games * sizeof(game_s));

Answer 2

你的努力值得称赞。您提供代码并善意地尝试理解为什么事情不起作用，但不幸的是，您的代码充满了错误。其中最重要的一点是您几乎立即调用 Undefined Behavior，尝试使用未初始化的 num_of_games 声明 VLA。从那时起，无论您在代码中做了什么，无论您是实际处理了某些东西还是 SegFaulted，都只是掷骰子。

display_inventory 中缺少输出（无论内存中实际存在什么）是由于将printf 语句放置在switch 语句的主体中。当您从switch 中选择break 时，您不仅会跳到default 的下方，还可以完全跳出switch。所以即使你的其余代码是正确的，你也永远不会产生输出。

fflush(stdin) 是错误的，它会在除windoze 之外的所有对象上调用未定义的行为。它只为世界其他地方的 seekable 流定义——不要使用它。相反，您可以定义一个简单的函数来清空stdin，然后根据需要调用它。

编译时，请始终在启用编译器警告的情况下进行编译，并且不要接受代码，直到它在没有警告的情况下干净地编译。要启用警告，请将 -Wall -Wextra 添加到您的 gcc 编译字符串中。 （添加-pedantic 以获得其他几个警告）。对于 VS（windoze 上的cl.exe），添加/Wall。对于clang，添加-Weverything。阅读并理解每个警告。他们将识别任何问题，以及它们发生的确切线路。您可以通过聆听编译器告诉您的内容来尽可能多地了解编码。

您的代码中的错误数量过多，无法逐项列出并说明每一点，因此我在下面包含了 cmets inline 来解决这些错误。

#include <stdio.h>
#include <stdlib.h>     /* for EXIT_FAILURE */
#include <string.h>

#define MAX 16

typedef enum genre_type { 
    action = 0, 
    rpg = 1, 
    simulation = 2,
    strategy = 3, 
    sports = 4
} genre_t;

typedef struct {
    char title[MAX];
    int num_sold;
    genre_t genre;
} game_s;

// suppose to use functions and enum list for determining the genre
void get_game_info (game_s *ptr);
void display_inventory (game_s *game, int num_of_games);
void fflush_stdin();

int main (void) {

    int num_of_games,
        c_game = 0,
        scnfrtn;        /* scanf return - must always check EOF */

    printf ("How many games are there in inventory? ");
    for (;;) {  /* loop until valid input or EOF (user cancels) */
        if ((scnfrtn = scanf ("%d", &num_of_games)) == 1) {
            fflush_stdin(); /* manually empty stdin */
            break;
        }
        else if (scnfrtn == EOF) {  /* user cancels? */
            fprintf (stderr, "user canceled input.\n");
            exit (EXIT_FAILURE);
        }
        /* handle error */
        fprintf (stderr, "error: invalid input.\n");
        fflush_stdin();
    }
    putchar ('\n');             /* don't printf a single-char */

    /* declare VLA only AFTER num_of_games has a value */
    game_s game[num_of_games];
    memset (game, 0, sizeof game);  /* optional, zero VLA */

    while (c_game < num_of_games) {
        putchar ('\n');
        get_game_info (&game[c_game]);
        c_game++;
    }
    putchar ('\n');

    display_inventory (game, num_of_games);

    return 0;
}

void get_game_info (game_s *ptr)
{
    int scnfrtn;        /* scanf return - must always check EOF */
    size_t len = 0;     /* strlen return is size_t */

    printf ("Title of game <maximum of 15 characters>: ");
    fgets (ptr->title, MAX, stdin); /* NEVER, NEVER, NEVER use gets */
    len = strlen (ptr->title);
    if (len && ptr->title[len-1] == '\n')   /* check for trailing \n */
        ptr->title[--len] = '\0';    /* overwrite with nul-character */
    else    /* warn of truncation */
        fprintf (stderr, "error: title too long, truncated.\n");

    for (;;) {  /* loop until valid input or EOF (user cancels) */
        printf ("Number sold: ");
        if ((scnfrtn = scanf ("%d", &ptr->num_sold)) == 1) {
            fflush_stdin();
            break;
        }
        else if (scnfrtn == EOF) {
            fprintf (stderr, "user canceled input.\n");
            exit (EXIT_FAILURE);
        }
        fprintf (stderr, "error: invalid input.\n");
        fflush_stdin();
    }

    for (;;) {  /* loop until valid input or EOF (user cancels) */
        printf ("Genre (0-action, 1-rpg, 2-simulation, "
                "3-strategy, 4-sports): ");
        if ((scnfrtn = scanf ("%d", (int*)&ptr->genre)) == 1) {
            fflush_stdin();
            break;        
        }
        else if (scnfrtn == EOF) {
            fprintf (stderr, "user canceled input.\n");
            exit (EXIT_FAILURE);
        }
        else if (ptr->genre > 4)    /* additional check for genre */
            fprintf (stderr, "error: invalid genre.\n");
        else
            fprintf (stderr, "error: invalid input.\n");

        fflush_stdin();
    }
}

void display_inventory (game_s *game, int num_of_games)
{
    int i;

    printf ("%11s%-24s %-24s %s\n========================="
            "==============================================\n", 
            " ", "Title","Quantity Sold", "Genre");
    for (i = 0; i < num_of_games; i++) {
        switch (game[i].genre) {
            case action:
                printf ("%-11s", "Action");
                break;
            case rpg:
                printf ("%-11s", "RPG");
                break;
            case simulation:
                printf ("%-11s", "Simulation");
                break;
            case strategy:
                printf ("%-11s", "Strategy");
                break;
            case sports:
                printf ("%-11s", "Sports");
                break;
            default:
                puts ("Not a choice. Try again");
                break;
        }
        printf ("%-24s %-24u %d\n", game[i].title,
                game[i].num_sold, game[i].genre);
    }
}

void fflush_stdin()
{
    for (int c = getchar(); c != '\n' && c != EOF; c = getchar()) {}
}

（注意：使用printf 带修饰符的最小字段来控制间距，而不是一堆tabs混在一起）

使用/输出示例

$ ./bin/gamegenre
How many games are there in inventory? 3


Title of game <maximum of 15 characters>: first title
Number sold: 12
Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): 2

Title of game <maximum of 15 characters>: second title
Number sold: 13
Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): 1

Title of game <maximum of 15 characters>: third title
Number sold: 14
Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): 3

           Title                    Quantity Sold            Genre
=======================================================================
Simulation first title              12                       2
RPG        second title             13                       1
Strategy   third title              14                       3

（注意：我不知道你打算把你的genre描述放在哪里，所以它们只是在上面每一行的开头输出）

查看一下，如果您还有其他问题，请告诉我。