如何检测用户是否插入带逗号的数据（以所需的格式）？

用户以以下格式插入数据：“[NAME]，[SURNAME]，[INDEX]”。错误代码：
0——一切都正确加载到结构中
1 -- 未正确加载到结构（用户未使用逗号或 p->name 出错）
2 -- 仅正确加载名称
3 -- 姓名正确加载（索引出错）

struct student_t
{
    char name[20];
    char surname[40];
    int index;
};

例子：
输入：约翰·迪普
错误代码：2

输入：约翰，深，999
错误代码：0

输入：NULL //（什么都没有）
错误代码：1
... 所以我无法检测用户是否插入例如：“John，Deep”（err 2）或“John，Deep，”（err 3）或“John，”（err 2），..（结果是 err 1；或者如果一切正常，则 err 0）
我的尝试：//edit1：使用这种方法的工作版本，进一步低于此方法。

char buffer[1024], *pch1, *pch2;
if (fgets(buffer,1024, stdin)!=NULL) 
{
    pch1=strchr(buffer, ',');
    pch2=strrchr(buffer, ',');

    if (pch1!=pch2 && pch1!=NULL) //detects if inserted are 2 different commas
    {
        char *name = strtok(buffer,","); // returns pointer to the beginning of the token
        if (name) {//the place where "," occurs, becomes a "NULL" character
            sscanf(name," %19s", p->name);  // skip leading spaces
            char *surname = strtok(NULL,",");
            if (surname) {
                sscanf(surname," %39s", p->surname); // skip leading spaces
                char *index = strtok(NULL,",");
                if (index) {
                    p->index = (int)strtol(index, NULL, 10);
                           } else {*err_code=3; return NULL;} //only NAME and SURNAME correctly, INDEX is loaded wrong
                         } else {*err_code=2; return NULL;} //only NAME loaded correctly
                  }
    } else  if (pch1==pch2 && pch1!=NULL) 
    {//but if there is 1 comma, input may be like: "John, Deep" so name'd be ok
            char *name = strtok(buffer,","); 
            if (name) { 
                sscanf(name," %19s", p->name);  
                char *surname = strtok(NULL,",");
                if (surname) {
                    sscanf(surname," %39s", p->surname); 
                    char *index = strtok(NULL,",");
                    if (index) {
                        p->index = (int)strtol(index, NULL, 10);
                               }else if (p->index==0||p->index==0||p->index==' ') {*err_code=2; return NULL;}
                             } 
                      } 

    } else {*err_code=1; return NULL;} //if there were 0 commas, err_code=1
}

if (p==NULL || p->name==NULL)
{
    *err_code=1;
    return NULL;
}
 if (p->surname && p->name==NULL)
{
    *err_code=2;
    return NULL;
}
//because the above "if" construction didn't work, I added another one here:
 if (p->index==NULL || p->index==0) //so if input was "John, Deep" then p->index should be NULL? 
{
    *err_code=3;
    return NULL;
}

//edit1：好的，这段代码对我有用，一切都按设想进行。然而它非常混乱，所以我会尝试在其他版本中采用和使用答案......

char buffer[1024], *pch1, *pch2;

if (fgets(buffer,1024, stdin)!=NULL) 
{
    pch1=strchr(buffer, ',');
    pch2=strrchr(buffer, ',');

    if (pch1!=pch2 && pch1!=NULL)
    {
        char *name = strtok(buffer,","); // returns pointer to the beginning of the token
        if (name) { //the place where "," is occured becomes a "NULL" character
            sscanf(name," %19s", p->name);  // skip leading spaces
            char *surname = strtok(NULL,",");
            if (surname) {
                sscanf(surname," %39[^\t\n]", p->surname); // skip leading spaces
                char *index = strtok(NULL,",");
                if (index) {
                    p->index = (int)strtol(index, NULL, 10);
                    if (p->index==0) {*err_code=3; return NULL;}
                           } //else {*err_code=3; return NULL;} //only NAME and SURNAME correctly, INDEX is loaded wrong
                         } else {*err_code=2; return NULL;} //only NAME loaded correctly
                  }
    } else  if (pch1==pch2 && pch1!=NULL)
    {
            char *name = strtok(buffer,","); // returns pointer to the beginning of the token
            if (name) { //the place where "," is occured becomes a "NULL" character
                sscanf(name," %19s", p->name);  // skip leading spaces
                char *surname = strtok(NULL,",");
                if (surname) {
                    sscanf(surname," %39[^\t\n]", p->surname); // skip leading spaces
                    char *index = strtok(NULL,",");
                    if (index) {
                        p->index = (int)strtol(index, NULL, 10);
                               } else if (p->index==0||p->index==' ') {*err_code=2; return NULL;} 
                             } else {*err_code=1; return NULL;} 
                                          } else {*err_code=2; return NULL;}

    } else {*err_code=1; return NULL;}
}

if (p==NULL || p->name==NULL)
{
    *err_code=1;
    return NULL;
}

我有一种感觉，它可以用一种完全不同的方式来完成……我会把所有的提示和答案放在心上，并尽我最大的努力去理解和学习它们。

//edit1：如果我丑陋的代码激怒了某人，我真的很乐意做一些园丁工作并剪掉一些恶魔灌木，以清理一下。我认为有些情况根本不需要它起作用......
附言。 （这是我之前问题的延续，其中输入的逗号被分配给结构：如何扫描逗号，但逗号未分配给结构？ C https://stackoverflow.com/questions/51343178/how-to-scanf-commas-but-with-commas-not-assigned-to-a-structure-c但在这个主题中，我询问以一种用户输入错误的信息的方式进行操作）

如果超出范围，这里有您需要的scanf族函数可以做到这一点，因为您想去除开头或结尾的空白字符name但仍想留出空间inside一个名字。恕我直言，您应该使用专用函数进行解析。代码可以是：

/* Find a string delimited with a character from delims.
 * Blanks at the beginning or the end of the string will be trimed out
 * At return, *end points one past the end of the string and
 * *next points after the delimiter (so delimiter will be next[-1])
 * Returns a pointer to the beginning of the string, or NULL if
 * no delimiter was found
 * */
const char* find(const char * start, char **end, char **next, const char *delims) {
    static const char blanks[] = " \t\r";
    start += strspn(start, blanks);     // trim blanks at the beginning
    *end = strpbrk(start, delims);      // search first delimiter
    if (end == NULL) {
        return NULL;
    }
    *next = *end + 1;                   // next find will start after the delimiter
    while(*end > start) {               // trim blanks at the end
        bool found = false;
        for (int i=0; i<sizeof(blanks); i++) {
            if ((*end)[-1] == blanks[i]) {
                --*end ;
                found = true;
                break;
            }
        }
        if (! found) break;
    }
    return start;
}
// parse a line to fill a student_t
struct student_t* getstruct(struct student_t *p, int *err_code) {
    char buffer[1024];
    *err_code = 1;       // be prepared to worst case
    *buffer = '\0';
    if (fgets(buffer,1024, stdin)!=NULL) 
    {
        char *end, *next;
        const char delims[] = ",\r\n";
        const char *name = find(buffer, &end, &next, delims) ; // returns pointer to the beginning of the token
        if (name && (next[-1] == ',')) {  // control the delimiter
            int l = end - name;
            if (l > 19) l = 19;
            memcpy(p->name, name, l);
            p->name[l] = '\0';
            *err_code = 2;                // Ok, we have a name followed with a comma
            const char *surname = find(next, &end, &next, delims);
            if (surname && (next[-1] == ',')) { // control delimiter
                int l = end - surname;
                if (l > 19) l = 19;
                memcpy(p->surname, surname, l);
                p->surname[l] = '\0';
                *err_code = 3;            // Ok, we have a name followed with a comma
                if (*end != ',') return NULL;
                const char *index = find(next, &end, &next, delims);
                if (index) {              // no need to control the delimiter: scanf will control  
                    char dummy[2];        // that there is no non blank char after the index
                    if (1 == sscanf(index, "%d%1s", &(p->index), dummy)) {
                        *err_code = 0;
                    }
                }
            }
        }
    }
    return (*err_code == 0) ? p : NULL;
}