c - The printf functions print something that shouldn't, why? -

as can see images attached below, adding second element top of list create strange behaviour printf function.

the function add list node is:

void add_queuenode_top(item a) {     if (head==null)     {         queueinit(a);     }     else     {         queueput_top(a);     }     return; }  void queueinit(item a) {     head=(link)malloc(sizeof(link*));     head->next=null;     head->item=a;     tail=head;     printf("coda iniziallizata...\n\n");  }  void queueput_top(item a) {     link tmp;     tmp=(link)malloc(sizeof(link*));     tmp->item=a;     tmp->next=head;     head=tmp;     return; } 

here functions handle items:

item fill_item() {     item a;     int i;     for(i=0; i<dim-1; i++)     {         a.stringa[i]=rand();     }     a.stringa[dim-1]='\0';     a.numero=rand();     printf("\noggetto generato: \n");     print_item(a);     return a; }  void print_item(item a) {     printf("\nstringa elemento: ");     printf("%s", a.stringa);     printf("\nnumero elemento:  %d\n", a.numero); } 

here's link codeblock project i'm editing. function print_item(item a) call "bugged" printf in item.c module, while functions generate list item inside list.c module.

any idea of can cause problem?

ps: i'm sorry captures located in italian

edit: definition of items:

typedef struct {     char stringa[dim];     int numero; } item; 

definition of link pointer:

typedef struct queuenode *link; 

definition of link structure:

struct queuenode     {         item item;         link next;     }; 

you have several bugs - i'll try go through , find more of them you, specific problem you're asking related code:

for(i=0; i<dim-1; i++) {     a.stringa[i]=rand(); } a.stringa[dim-1]='\0'; 

you're putting random number in each character - many of them may not interesting or printable characters in character set. that's why crazy output you're seeing. if want put random printable characters string, in more character-set-aware way.

some more problems:

1. these allocation lines wrong:

   head=(link)malloc(sizeof(link*)); tmp=(link)malloc(sizeof(link*)); 

   they should be:

   head = malloc(sizeof(struct queuenode)); tmp = malloc(sizeof(struct queuenode)); 

   that is, should allocate enough size entire struct queuenode, not pointer one. (or pointer pointer one, had). hiding pointer type inside typedef typedef struct queuenode *link; 1 of controversial style choices - prefer not to, since confuses issues 1 pretty fast.

2. you're passing around lot of structures value in program. that's fine , valid c, it's bit non-idiomatic. people pass around pointers instead. if structure grows appreciable size, performance can start suffer badly result of of implicit memory copying going on.