为什么这个程序不起作用？

Question

当我在C编程语言上工作时，我想做一个小程序来修改以前的知识点。这就是这个程序，它似乎有一些问题。

这个程序应该从输入中收集信息，并以一种格式在文件"reg.txt“中打印出来。

但是，在输入第一行并按enter键后，程序就退出了，但是我不知道它到底出了什么问题。

#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的建议，并且我的目标是检查'sscanf‘的返回值。奇怪的是，程序并没有真正到达“printf”部分。我想这个循环可能有问题吗？

#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

即使在确保line已经分配了内存之后，当sscanf尝试向people[0].name和people[0].surname写入时，您的sscanf上也会出现分段错误，因为这些指针将是未定义的。

您需要静态或动态地为这些字符串分配内存(使用malloc)。

打印日志语句也有助于收集一些洞察力。

#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;
}

编辑:因为gets是不推荐的，这里有一个fget替代方案。关于gets的进一步阅读：Why is the gets function so dangerous that it should not be used?

编辑:还添加了chux的缓冲区溢出保护。关于用scanf：Read no more than size of string with scanf()防止缓冲区溢出的进一步解读

#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

在使用line和gets之前，您需要分配内存。

#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;
}