Why doesn't this program print the name? - c

Question

I’m trying to make a program that receives a text from a file where its lines are a first name, a last name and a note. I want to return the ordered lines: first the students with a grade lower than 5 and after the students passed in order of appearance in the file. The problem is that I can’t print the names and I don’t know what the fault is. The main code is as follows:
int main(int argc, char *argv[])
{
char line[MaxLinea+1];
char *name;
char *surname;
lista_notas *mi_lista = NULL;
int i, blank, grade;
FILE *archivo = fopen(argv[1], "r");
while(fgets(line, MaxLinea, archivo)) //recorrer linea fich
{
grade = get_grade(line);
if (grade < 5) //Insertar en la lista
{
name = get_name(line);
surname = get_surname(line);
insertar(&mi_lista, name, surname, grade);
}
}
fclose(archivo);
archivo = fopen(argv[1], "r");
while(fgets(line, MaxLinea, archivo)) //recorrer linea fich
{
grade = get_grade(line);
if (grade > 4) //Insertar en la lista
{
name = get_name(line);
surname = get_surname(line);
insertar(&mi_lista, name, surname, grade);
}
}
mostrar_lista(mi_lista);
free_lista(mi_lista);
//system("leaks a.out");
return 0;
}
The get_name function is:
char *get_name(char *line)
{
int i;
char *name = malloc(51);
if (name == NULL)
exit(71);
i = 0;
while(line[i] != ' ')
name[i] = line[i++];
name[i] = 0;
return name;
}
If the program receives a fich.txt which content is:
Nombre1 Apellido1 8
Nombre2 Apellido2 2
Nombre3 Apellido3 6
The output must be:
Nombre2 Apellido2 2
Nombre1 Apellido1 8
Nombre3 Apellido3 6
but instead, it is:
Apellido2 2
Apellido1 8
Apellido3 6
Thanks for your help!
The full code is:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MaxLinea 154
//Tamaño máximo linea = 50 (nombre) + 100 (apellido) + 2 (nota máx 10)
// + 2 espacios + caracter nulo? = 155
typedef struct notas{
char *nombre;
char *apellido;
int nota;
struct notas *siguiente;
} lista_notas;
int get_grade(char *line);
char *get_name(char *line);
char *get_surname(char *line);
void insertar(lista_notas **ptr, char *name, char *surname, int grade);
void mostrar_lista(lista_notas *ptr);
void free_lista(lista_notas *ptr);
int main(int argc, char *argv[])
{
char line[MaxLinea+1];
char *name;
char *surname;
lista_notas *mi_lista = NULL;
int i, blank, grade;
FILE *archivo = fopen(argv[1], "r");
while(fgets(line, MaxLinea, archivo)) //recorrer linea fich
{
grade = get_grade(line);
if (grade < 5) //Insertar en la lista
{
name = get_name(line);
surname = get_surname(line);
insertar(&mi_lista, name, surname, grade);
}
}
fclose(archivo);
archivo = fopen(argv[1], "r");
while(fgets(line, MaxLinea, archivo)) //recorrer linea fich
{
grade = get_grade(line);
if (grade > 4) //Insertar en la lista
{
name = get_name(line);
surname = get_surname(line);
insertar(&mi_lista, name, surname, grade);
}
}
mostrar_lista(mi_lista);
free_lista(mi_lista);
//system("leaks a.out");
return 0;
}
void insertar(lista_notas **ptr, char *name, char *surname, int grade)
{
lista_notas *p1, *p2;
p1 = *ptr;
if(p1 == NULL)
{
p1 = malloc(sizeof(lista_notas));//y si usamos calloc ¿qué cambia?
if (p1 == NULL)
exit(71);
if (p1 != NULL)
{
p1->nombre = name;
p1->apellido = surname;
p1->nota = grade;
p1->siguiente = NULL;
*ptr = p1;
}
}
else
{
while(p1->siguiente != NULL)//recorrer la lista hasta el último
p1 = p1->siguiente;
p2 = malloc(sizeof(lista_notas));//y si usamos calloc ¿qué cambia?
if (p2 == NULL)
exit(71);
if(p2 != NULL)
{
p2->nombre = name;
p2->apellido = surname;
p2->nota = grade;
p2->siguiente = NULL;
p1->siguiente = p2;
}
}
}
void mostrar_lista(lista_notas *ptr)
{
while(ptr != NULL)
{
printf("%s ",ptr->nombre);
printf("%s ",ptr->apellido);
printf("%d\n",ptr->nota);
ptr = ptr->siguiente;
}
/* printf("\n");*/
}
void free_lista(lista_notas *ptr)
{
lista_notas *aux = ptr;
lista_notas *aux2;
while(aux != NULL)
{
aux2 = aux;
aux = aux->siguiente;
free(aux2->nombre);
free(aux2->apellido);
free(aux2);
}
}
int get_grade(char *line)
{
int i, blank, num;
i = 0;
blank = 0;
while(line[i] != '\0')
{
if (blank == 2) //sacar la nota
{
num = atoi(&line[i]);
blank++;
}
else if(line[i] == ' ')
blank++;
i++;
}
return num;
}
char *get_name(char *line)
{
int i;
char *name = malloc(51);
if (name == NULL)
exit(71);
i = 0;
while(line[i] != ' ')
name[i] = line[i++];
name[i] = 0;
return name;
}
char *get_surname(char *line)
{
int i, j;
char *surname = malloc(101);
if (surname == NULL)
exit(71);
i = 0;
j = 0;
while(line[i] != ' ')
i++;
while(line[++i] != ' ')
surname[j++] = line[i];
surname[j] = 0;
return surname;
}

Answer 1

At least these problems:
++ not sequenced
name[i] = line[i++]; is bad code. The i++may occur before, after, (or even during) name[i]. Result: undefined behavior (UB). #paddy
Limited size
char *name = malloc(51); does not need to use the magic number 51.
May run off end
while(line[i] != ' ') leads to trouble when line[] lacks a ' '.
Alternative (like OP's code)
char *get_name(char *line) {
size_t i = 0;
while(line[i] != ' ' && line[i] != '\0') {
i++;
}
char *name = malloc(i + 1);
if (name == NULL) {
exit(71);
}
for (size_t j = 0; j < i; j++) {
name[j] = line[j];
}
name[i] = 0;
return name;
}
Or perhaps using standard efficient library functions
char *get_name(const char *line) {
size_t token_length = strcspn(line, " ");
char *name = malloc(token_length + 1);
if (name == NULL) {
exit(71); // Consider a named macro/enum here rather than a magic 71
}
name[token_length] = '\0';
return memcpy(name, line, token_length);
}
Other issues
Off by 1
// fgets(line, MaxLinea, archivo)
fgets(line, sizeof line, archivo)
Advanced: Assuming first, last names do not include spaces
Consider first names like "Betty Jo" and last names like Lloyd Webber
Some names are longer than 51.