Bdtjtk

I want to write functions to get and print data entered by a user. Idea is to to have name and a last name as pointers, pointers to variable size strings. What is wrong with code? What am I doing wrong? Alternatives?

#include <stdio.h>

#include <stdlib.h>

typedef struct {

   char *name;

   char *lastname;

   int marks[5];

} Student;

void setS(Student *s);

void getS(Student *s);



int main()

{

   Student st;

   getS(&st);

   setS(&st);

   return 0;

 }



 void setS(Student *s){

    int i;

    printf("Name: %st", s->name);

    printf("last Name: %st", s->lastname);

    for(i=0; i<5; i++)

        printf("%3d", s->marks[i]);

    printf("n");

 }

 void getS(Student *s){

    int i;

    printf("Enter namen");

    gets(s->name);

    printf("Enter last namen");

    gets(s->lastname);

    printf("Enter marksn");

    for(i=0; i<5; i++)    

       scanf("%d", &s->marks[i]);

    printf("n");

  }

What is wrong with code? What am I doing wrong?

gets(s->name); attempts to read user input into s->name. s->name is a char * that has not yet been assigned. gets() attempts to save data to who-knows-where? Result: undefined behavior (UB).

Alternatives?

Read into a buffer and then allocated memory for a copy.

Tip: As you can, avoid scanf(), gets() for user input and use fgets(). C - scanf() vs gets() vs fgets().

Some code to provide an idea.

#define NAME_N 100



// return 1 on success

// return EOF on end-of-file

// return 0 other errors

int getS(Student *s) {

  *s = (Student) {NULL, NULL, {0}}; // pre-fill with default values.



  char buffer[NAME_N];

  printf("Enter namen");

  if (fgets(buffer, sizeof buffer, stdin) == NULL) {

    return EOF;

  }

  trim(buffer);

  if (!validate_name(buffer)) {

    return 0;

  }

  s->name = strdup(buffer);



  printf("Enter last namen");

  if (fgets(buffer, sizeof buffer, stdin) == NULL) {

    return EOF;

  }

  trim(buffer);

  if (!validate_name(buffer)) {

    return 0;

  }

  s->lastname = strdup(buffer);



  printf("Enter marksn");

  for (int i = 0; i < 5; i++) {

    if (fgets(buffer, sizeof buffer, stdin) == NULL) {

      return EOF;

    }

    if (sscanf(buffer, "%d", &s->marks[i]) != 1) {

      return 0;

    }

  }

  return 1;

}

trim() is your function to trim leading/trailing/excessive white-spaces. See also How do I trim leading/trailing whitespace in a standard way?.

strdup() is not C standard yet very commonly available string duplication function that allocated memory and copies. Sample code

validate_name() is placeholder code to insure some sanity in the name. Be generous in what is acceptable. Commonly acceptable characters in a name include
[A-Z, a-z, '-', ''', ' ', '.'] and many others: What are all of the allowable characters for people's names?.

Example:

// Fail a zero length name or one with controls characters in it.

bool validate_name(const char *name) {

  if (*name == '') return false;

  while (*name) {

    if (iscntrl((unsigned char) *name)) return false;

    name++;

  }

  return true;

}