c - C中的结构排列

Question

我正在尝试制作一个程序，按人员 ID 排列我的结构。 我使用 long double 因为 ID 有 20 位数字长。 例如，如果我介绍 3 个人:

1.Alex Alex / id = 219(...)
2.John John / id = 200(...)
3.Robert Robert / id = 199(...)

我希望我的程序重新排列，让罗伯特排在第一位，约翰排在第二位，亚历克斯排在第三位。 我在“for”结构上遇到问题 - 我不知道如何交换两个结构，因为我结合了字符和整数。

typedef struct 
{
    char name;
    char prename;
    long double id;
    int j;
} PERSON;

int main() 
{
    int n,i,j;
    printf ("How many people = ");
    scanf("%d", &n);
    PERSON v[n];
    for(i=1;i<=n;i++)
    {
        printf("For person number nr. %d\n", i);
        printf("name = ");
        scanf("%s", &v[i].name);
        printf("Prename = ");
        scanf("%s", &v[i].prename);
        printf("id = ");
        scanf("%d", &v[i].id);
    }

    for(int i=0; i<n; i++)
    {
        for(int j=0; j<n-1; j++)
        {
            if( v[i].id > v[j+1].id )
            {
                int temp = v[j].id;
                char temp2[100];
                char temp3[100];

                strcpy(v[j].prename,temp3);
                strcpy(v[j].name,temp2);
                v[j].id = v[j+1].id;
                v[j+1].id = temp;
            }
        }
    }

    return;
}

Answer 1

好的，因为您在这里完成的很多事情对于新的 C 开发人员来说并不明显，我想指出它们以帮助您学习:

typedef struct 
{
    // These need to be arrays if they are to be strings
    // Preferably using a constant for size or dynamic
    // if you want them to be variable sized to match input.
    char name;
    char prename;
    // Do not use floating point numbers to represent integer values.  
    // IRL, you'd use a library, but here, you may want to use an array of 
    // some sort of integer type instead.
    long double id;  

    // This is a really poor name for a struct variable and probably shouldn't be here.
    int j;
} PERSON;

int main() 
{
    int n,i,j;
    printf ("How many people = ");
    // Dropping raw output from scanf into a memory allocation is crazy dangerous.
    // At least error check the results to be sure it is meaningful.
    scanf("%d", &n);
    // This is a variable length array and often is not supported directly.
    // You probably want to use a malloc()/free() pair to handle this.
    // (Update: VLA is now part of newer standards, but are not safe because they cannot fail gracefully on out of memory.)
    PERSON v[n];

    // Anytime in C I see an array start at 1 and use <= for condition, I get very nervous because
    // it tends to lead to indexing errors.
    for(i=1;i<=n;i++)
    {
        printf("For person number nr. %d\n", i);
        printf("name = ");

        // Oops - and this is why.  You just skipped the first entry at 0
        // and will overwrite memory on the last loop.
        // Also, scanf into a string without a length can blow up memory...
        scanf("%s", &v[i].name);
        printf("Prename = ");
        // Ditto
        scanf("%s", &v[i].prename);
        printf("id = ");
        // Ditto - worse because you've crossed your types - %d doesn't go into a long double.
        scanf("%d", &v[i].id);
    }

    // Should be its own function to make it easier to swap later to a better sort.
    for(int i=0; i<n; i++)
    {
        // Bubble sort usually wants j=i here.
        for(int j=0; j<n-1; j++)
        {
            if( v[i].id > v[j+1].id )
            {
                // Make a swap function here.  Makes it clearer what you want to do.
                int temp = v[j].id;

                // What is 100?  How do you know that is enough?
                // These are called magic numbers and lead to code death.
                char temp2[100];
                char temp3[100];

                // Ah, strcpy - 3 things wrong here.
                // 1 - You have the parameters backwards - you are copying temp3 to your struct.
                // 2 - You have no way to know if the destination will fit the source because it copies until it finds a '\0' - very dangerous.
                // 3 - Because your parameters are backwards and temp123 is not initialized, this very well could copy forever.
                // strncpy (also crazy dangerous) at the least should be used and consider using better means like strlcpy() and such.
                strcpy(v[j].prename,temp3);
                strcpy(v[j].name,temp2);
                v[j].id = v[j+1].id;
                v[j+1].id = temp;

                // You kinda forgot to swap the strings, but the program is already dead so no worries.
            }
        }
    }

    // Please enable compiler warnings - you must return a value here.
    return;
}

说真的，我确定我错过了一些其他的东西，但这对于免费的互联网代码审查和学习 session 来说已经足够了。 :)

关于 strcpy() 和 strncpy() 的信息 Why is strncpy insecure?

关于 scanf() 安全的信息 How to prevent scanf causing a buffer overflow in C?

关于可变长度数组安全的信息: Is it safe to use variable-length arrays?