How to fix conditional jump? - c

Question

I have a problem with, i think, function INPUT. But i can't understand how to fix it
[functions code]
typedef struct Item {
int data;
struct Item* next;
} Item;
typedef struct Queue{
Item* head;
Item* tail;
} Queue;
void input(Queue* list,int* stroka) {
Item* new = (Item*)malloc(sizeof(Item));
new->data = *stroka;
new->next = NULL;
if (!list->head) {
list->head = new;
list->tail = new;
} else {
list->tail->next = new;
list->tail = new;
}
}
int main() {
int stroka;
Queue* list = (Queue*)malloc(sizeof(Queue));
while(stroka != EOF) {
stroka = getchar();
input(list, &stroka);
}
printf("\n");
print(list);
}
[valgrind message]
Conditional jump or move depends on uninitialised value(s)
==29969== at 0x10931A: input ()
==29969== by 0x1093CF: main ()
==29969== Uninitialised value was created by a heap allocation
==29969== at 0x48427B5: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==29969== by 0x1093B1: main ()
tried to change some blocks of code but i didn't come to anything

Answer 1

In the while loop you are using an uninitialized object of the type int and trying it to compare with a null pointer
int stroka;
Queue* list = (Queue*)malloc(sizeof(Queue));
while(stroka != EOF) {
stroka = getchar();
input(list, &stroka);
}
that does not make sense.
And there is no need to allocate dynamically an object of the type Queue.
Also instead of getchar it is much better to use scanf to enter integers instead of single characters that will be interpreted as integers including the new line character '\n'..
Also there is no any sense to pass the object stroke through a pointer to the function.
The function should be declared and defined the following way
int input( Queue* list, int data )
{
Item *new_item = malloc( sizeof( *new_item ) );
int success = new_item != NULL;
if ( success )
{
new_item->data = data;
new_item->next = NULL;
if ( list->head == NULL )
{
list->head = new_item;
}
else
{
list->tail->next = new_item;
}
list->tail = new_item;
}
return success;
}
And in main you can write for example
int main( void )
{
Queue list = { .head = NULL, .tail = NULL };
for ( int data; scanf( "%d", &data ) == 1; )
{
input( &list, data );
}
printf("\n");
print(list);
}
If you want to enter characters then declare the function like
int input( Queue* list, char data );
and in main write
for ( char data; scanf( " %c", &data ) == 1; )
{
input( &list, data );
}
Pay attention to the space in the format string in the call of scanf. It allows to skip white space characters.
And do not forget to write a function that will free all the allocated memory when the list will nit be required any more.