為什么該程序不起作用？

Question

當我使用C編程語言時 ，我想做一個小程序來修改這些以前的知識點。 這是一個似乎有問題的程序。

該程序應該從輸入中收集信息，並以格式將其打印在“ reg.txt”文件中。

但是，在鍵入第一行並按Enter鍵之后，該程序退出，但是我無法弄清楚它出了什么問題。

#include <stdio.h>

int main()
{
    FILE *fp;
    struct profile
    {
        char *name;
        char *surname;
        int year;
        int month;
        int day;
    } people[10];
    int temp;
    int i = 0;
    char *line;


    fp = fopen("reg.txt", "a");
    while (fgets(line, 256, stdin)
    {
        sscanf(line, "%s %s %d/%d/%d", people[i].name, people[i].surname, &(people[i].year), &(people[i].month), &(people[i].day));
        ++i;
    }
    temp = i-1;

    for (i = 0; i <= temp; ++i)
        fprintf(fp, "NAME: %s %s\nBIRTHDAY: %d/%d/%d\n", people[i].name, people[i].surname, people[i].year, people[i].month, people[i].day);

    fclose(fp);
    return 0;
}

---

我接受了Ed Heal的建議，目的是檢查'sscanf'的返回值。 奇怪的是該程序並沒有真正到達“ printf”部分。 我以為循環可能存在一些問題？

#include <stdio.h>

int main()
{
    FILE *fp;
    void filecopy(FILE *, FILE *);
    struct profile
    {
        char *name;
        char *surname;
        int year;
        int month;
        int day;
    } people[10];
    int temp;
    int i = 0;
    char *line;
    int j;


    fp = fopen("reg.txt", "a");
    while (fgets(line, 256, stdin) != NULL)
    {
        j = sscanf(line, "%s %s %d/%d/%d", people[i].name, people[i].surname, &(people[i].year), &(people[i].month), &(people[i].day));
        ++i;
    }
    temp = i-1;

    //for (i = 0; i <= temp; ++i)
    //  fprintf(fp, "NAME: %s %s\nBIRTHDAY: %d/%d/%d\n", people[i].name, people[i].surname, people[i].year, people[i].month, people[i].day);

    printf("%d",j);
    fclose(fp);
    return 0;
}

Answer 1

即使在確定line已分配內存之后，當sscanf嘗試寫入people[0].name和people[0].surname時，也應該在它的段上出現段people[0].surname因為這些指針將是未定義的。

您需要為這些字符串靜態或動態分配內存（使用malloc）。

打印日志語句也可以幫助您收集一些見解。

#include <stdio.h>

int main()
{
    FILE *fp;
    typedef struct
    {
        char name[64];
        char surname[64];
        int year;
        int month;
        int day;
    } profile;
    profile people[10];

    int temp;
    int i = 0;
    char line[512];

    printf("Starting profile line parser...\n");
    printf("Please enter up to 10 people in the format: (name surname year/month/day)\n");
    printf("Enter EOF to exit. (Linux: CTRL+D     Windows CTRL+Z)\n");
    fp = fopen("reg.txt", "a");
    while (gets(line) != NULL)
    {
        sscanf(line, "%63s %63s %d/%d/%d", people[i].name, people[i].surname, &(people[i].year), &(people[i].month), &(people[i].day));
        ++i;
    }
    printf("Processed %d lines.\n", i);
    temp = i-1;
    for (i = 0; i <= temp; ++i)
    {
        fprintf(fp, "NAME: %s %s\nBIRTHDAY: %d/%d/%d\n", people[i].name, people[i].surname, people[i].year, people[i].month, people[i].day);
    }

    fclose(fp);
    printf("Done with profile line parser...\n");
    return 0;
}

編輯：因為不贊成使用gets，所以這里是fgets的替代方案。 關於gets的進一步閱讀： 為什么gets函數如此危險，以至於不應該使用它？

編輯：還添加了chux的緩沖區溢出保護。 有關使用scanf防止緩沖區溢出的更多信息 ： 使用scanf（）讀取的字符串大小不超過

#include <stdio.h>

int main()
{
    FILE *fp;
    typedef struct
    {
        char name[64];
        char surname[64];
        int year;
        int month;
        int day;
    } profile;
    profile people[10];

    int temp;
    int i = 0;
    char line[512];

    printf("Starting profile line parser...\n");
    printf("Please enter up to 10 people in the format: (name surname year/month/day)\n");
    printf("Enter EOF to exit. (Linux: CTRL+D     Windows CTRL+Z)\n");
    fp = fopen("reg.txt", "a");
    while (fgets(line, 512, stdin) != NULL)
    {
        sscanf(line, "%63s %63s %d/%d/%d", people[i].name, people[i].surname, &(people[i].year), &(people[i].month), &(people[i].day));
        ++i;
    }
    printf("Processed %d lines.\n", i);
    temp = i-1;
    for (i = 0; i <= temp; ++i)
    {
        fprintf(fp, "NAME: %s %s\nBIRTHDAY: %d/%d/%d\n", people[i].name, people[i].surname, people[i].year, people[i].month, people[i].day);
    }
    printf("Done with profile line parser...\n");
    fclose(fp);
    return 0;
}

Answer 2

您需要在使用前分配內存line與gets

#include <stdio.h>

int main()
{
    FILE *fp;
    struct profile
    {
        char *name;
        char *surname;
        int year;
        int month;
        int day;
    };
    struct profile people[10];
    int temp;
    int i = 0;
    char line[256]; //you can also do dynamic allocation by using malloc

    fp = fopen("reg.txt", "a");
   // while (gets(line) != NULL) //use fgets instead gets
    while( fgets(line, 256, stdin) ) //specify required buffer len
    {
        sscanf(line, "%s %s %d/%d/%d", people[i].name, people[i].surname, &(people[i].year), &(people[i].month), &(people[i].day));
        ++i;
    }
    temp = i-1;

    for (i = 0; i <= temp; ++i)
        fprintf(fp, "NAME: %s %s\nBIRTHDAY: %d/%d/%d\n", people[i].name, people[i].surname, people[i].year, people[i].month, people[i].day);

    fclose(fp);
    return 0;
}