I'm trying to create an array of Product structs and then print the name and code of each Product in the array, but I keep getting a segmentation fault. I have tried to insert each value without a loop and then printing, and it works, but I'd like to automate it. The function fill_products fills the products array according to the user's input, and the select_products prints each name-code pair for the entire array.
This is my code:
#include <stdio.h>
#include <stdlib.h>
typedef struct
{
int code;
char *name;
float price;
} Product;
void select_products(Product *products, int len)
{
int i;
printf("%-30s%s\n", "Name", "Code");
for (i = 0; i < len; i++)
{
printf("%-30s%d\n", products[i].name, products[i].code);
}
return;
}
void fill_products(Product *products, int len)
{
int i, code;
char *name;
float price;
for (i = 0; i < len; i++)
{
printf("Insert product name (%d / %d): ", i + 1, len);
scanf("%s", &name);
printf("Insert product price (%d / %d): ", i + 1, len);
scanf("%f", &price);
products[i].code = i;
products[i].name = name;
products[i].price = price;
}
return;
}
int is_alloc(Product *products)
{
if (products == NULL)
{
printf("Error: memory allocation unsuccessful.\n");
}
return products != NULL;
}
int main(void)
{
int len, n_bytes;
Product *products;
printf("Insert length of array: ");
scanf("%d", &len);
n_bytes = sizeof *products * len;
products = malloc(n_bytes);
if(!is_alloc(products))
{
exit(0);
}
fill_products(products, len);
select_products(products, len);
free(products);
return 0;
}
I keep getting a segmentation fault.
Please enable compiler warnings, and pay attention to them.
This code:
char *name;
...
scanf("%s", &name);
is bogus and doesn't do at all what you intend.
You must either allocate space for name separately (and then not forget to free() it), or make that space available in the Product structure like so:
typedef struct
{
int code;
char name[100];
float price;
} Product;
(this assumes there is a reasonable limit on name length).
Related
I am trying to free the memory allocated by my getSongInfo function, I have tried using a pointer to the function call but I get an error "cannt assign int to type int*" error. Any help would be great as the current way I have seems like it may work, but I might be completely wrong. Thanks!
Original Attempt:
int *memPtr = NULL
memPtr = getSongInfo(&fillPtr[arrayCounter], tempArtist[counter], tempSong[counter]);
Gives error!
Current Attempt:
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#pragma warning(disable:4996)
int getSongInfo(struct songInfo *pFillInfo, char *artistName, char *songName);
void printSongInfo(struct songInfo songList[10]);
struct songInfo {
char *songArtist;
char *songTitle;
};
int main(void)
{
struct songInfo *fillPtr;
struct songInfo songList[10];
fillPtr = &songList[0];
char tempArtist[10][30];
char tempSong[10][30];
int *memPtr = NULL;
int i = 0;
int counter = 0;
int arrayCounter = 0;
while (counter != 10)
{
printf("Please enter the artist name: ");
fgets(tempArtist[counter], sizeof(tempArtist[counter]), stdin);
tempArtist[counter][strcspn(tempArtist[counter], "\n")] = 0;
printf("Please enter the song name: ");
fgets(tempSong[counter], sizeof(tempSong[counter]), stdin);
tempSong[counter][strcspn(tempSong[counter], "\n")] = 0;
getSongInfo(&fillPtr[arrayCounter], tempArtist[counter], tempSong[counter]);
printf("Song and Artist Captured! \n");
counter++;
arrayCounter++;
}
printSongInfo(fillPtr);
free(fillPtr->songArtist);
free(fillPtr->songTitle);
}
int getSongInfo(struct songInfo *pFillInfo, char *artistName, char *songName)
{
pFillInfo->songArtist = (char*)malloc(strlen(artistName) + 1);
pFillInfo->songTitle = (char*)malloc(strlen(songName) + 1);
strcpy(pFillInfo->songArtist, artistName);
strcpy(pFillInfo->songTitle, songName);
return 1;
}
void printSongInfo(struct songInfo songList[10])
{
int counter = 0;
while (counter != 10)
{
printf("%-35s %-35s\n", songList[counter].songArtist, songList[counter].songTitle);
counter++;
}
}
Your getSongInfo function does not return a pointer, so attempting to put the return value into a variable and then free it is pointless. The pointers in question are inside the struct songInfo, specifically, the fillPtr variable (which is actually redundant, since songList and fillPtr point to the same location).
In addition, please be aware that strcspn will not always return a valid index. If it does not find a match, it will return the length of the first argument.
I think this is more like what you are trying to do:
int main(void)
{
const int numSongs = 10;
struct songInfo songList[numSongs];
char tempArtist[30];
char tempSong[30];
int i;
int newline_idx;
for (i = 0; i < numSongs; ++i)
{
printf("Please enter the artist name: ");
fgets(tempArtist, sizeof(tempArtist), stdin);
newline_idx = strcspn(tempArtist, "\n");
if (newline_idx < sizeof(tempArtist))
tempArtist[newline_idx] = 0;
printf("Please enter the song name: ");
fgets(tempSong, sizeof(tempSong), stdin);
newline_idx = strcspn(tempSong, "\n");
if (newline_idx < sizeof(tempSong))
tempSong[newline_idx] = 0;
getSongInfo(&songList[i], tempArtist, tempSong);
printf("Song and Artist Captured! \n");
}
for (i = 0; i < numSongs; ++i)
{
free(songList[i].songArtist);
free(songList[i].songTitle);
}
}
You might consider separating the code for free()ing each struct into its own function.
You might also consider heeding that compiler warning instead of ignoring it, as Bodo commented. Careless handling of strings from stdin is dangerous.
Hi I'm inputting a structure of a family with children with those two structures:
typedef struct person {
int id;
char* firstName;
int age;
}person;
typedef struct family {
char* lastName;
person father, mother;
person* children;
int numChildren;
}family;
EDIT: this is the edited function and it still crashes :
int initializeHouse(family **pdata)
{
char temp[SIZE];
int size, i, j;
printf("enter the number of families\n");
scanf("%d", &size);
*pdata = (family*)malloc(sizeof( family)*size);
for (i = 0; i<size; i++)
{
printf("Please enter the last name\n");
scanf("%s", temp);
(*pdata)[i].lastName = (char*)malloc(sizeof(char)* (strlen(temp) + 1));
strcpy(pdata[i]->lastName, temp);
printf("Enter the fathers first name\n");
scanf("%s", temp);
initPerson(temp, &pdata[i]->father.firstName);
printf("enter the fathers ID\n");
scanf("%d", &pdata[i]->father.id);
printf("Enter the fathers age\n");
scanf("%d", &pdata[i]->father.age);
printf("Enter the mothers first name\n");
scanf("%s", temp);
initPerson(temp, &pdata[i]->mother.firstName);
printf("enter the mothers ID\n");
scanf("%d", &pdata[i]->mother.id);
printf("Enter the mothers age\n");
scanf("%d", &pdata[i]->mother.age);
printf("enter the number of children");
scanf("%d", &pdata[i]->numChildren);
(*pdata)[i].children= (person*)malloc(sizeof(person)*(pdata[i]->numChildren));
for (j = 0; j<pdata[i]->numChildren; j++)
{
printf("enter the kids name\n");
scanf("%s", temp);
initPerson(temp, &pdata[i]->children[j].firstName);
printf("enter the kids ID\n");
scanf("%d", &pdata[i]->children[j].id);
printf("Enter the kids age\n");
scanf("%d", &pdata[i]->children[j].age);
}
}
return size;
}
void initPerson(char* str, char** fam)
{
*fam = (char*)malloc(sizeof(char)*(strlen(str) + 1));
strcpy(*fam, str);
}
EDIT: I changed the code and it still doesn't work, and it requires me to write some description so here it is ..
int main() {
int size;
family *a = NULL;
size=initializeHouse(&a);
}
declares a pointer to a family structure. When you pass it's address
size = initializeHouse(&a);
the function gets it as a family**
Okay, we're all on the same page to this point. When you allocate the target of that pointer
*pdata = malloc(sizeof(family) * size);
then *pdata points to an allocated array of structs, not pointers to those structs. Each struct is accessed by (*pdata)[i], which means -> dereference the double pointer pdata to get the address of the first element in the array, then access the array element with a subscript.
So your assignment should be
(*pdata)[i].lastName = malloc(sizeof(char)* (strlen(temp) + 1));
You use the dot . operator to access the members, because the result of the subscript access is a struct, not a pointer to a struct.
This little example using (*pdata)[i]. doesn't crash.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 40
typedef struct person {
int id;
char* firstName;
int age;
}person;
typedef struct family {
char* lastName;
person father, mother;
person* children;
int numChildren;
}family;
int initializeHouse(family **pdata)
{
char temp[SIZE];
int size, i, j;
printf("enter the number of families\n");
scanf("%d", &size);
*pdata = malloc(sizeof(family)*size);
for (i = 0; i<size; i++)
{
printf("Please enter the last name\n");
scanf("%39s", temp);
(*pdata)[i].lastName = malloc(sizeof(char)* (strlen(temp) + 1));
strcpy ( (*pdata)[i].lastName, temp);
}
return size;
}
int main ( void) {
int size;
family *a;
size=initializeHouse(&a);
}
It's important that you understand the memory layout.
family *fam;
family **pdata = &fam;
*pdata = (family*)malloc(sizeof(family)*size);
You have essentialy this: fam is a uninitialized pointer of type family.
pdata is a double pointer initialized with the address of fam. The malloc
call allocates space for size family-objects. By doing *pdata = malloc(...)
you are initializing fam.
This is the basic memory layout you have. base is the address returned by
malloc. slf is the size of struct family object, fpl is the size of a
pointer to a struct family object.
base = address returned by malloc
sfl = sizeof(struct family)
fpl = sizeof(struct family*)
base + 0 base + slf base + 2 * slf
+-----------------+------------------+------------------+
|struct family | struct family | struct family |
+-----------------+------------------+------------------+
base + 0 base + fpl base + 2*fpl base + 3*fpl base + 4*fpl
+------------+------------+------------+------------+-----------+
| pdata[0] | pdata[1] | pdata[2] | pdata[3] | pdata[4] |
+------------+------------+------------+------------+-----------+
The first row shows the memory in terms on struct family objects, the second
row shows you the same memory in terms on pointers (to struct family object).
This is very important distinction, because pdata[i] returns you a
pointer, not the object.
Remember pdata is a double pointer, pdata[i] is the equivalent to pdata + i,
that is the ith pointer begining at base.
Because the size of an struct family is defintitely different that the size of
a pointer, you see that the block don't align, that means
base + slf != base + fpl.
In the first iteration you are lucky, because pdata[0] and (*pdata)[0] are
the same. But pdata[1] and *(pdata)[1] are not the same. So doing
pdata[1]->lastname (instead of (*pdata)[1].lastname) you are accessing at a
wrong location in you allocated memory.
The easiest way to fix you code would be to change the pdata[i] in (*pdata)[i] as shown
in user3121023's answer.
edit
I see that user3121023 has retracted his answer. Basically it did:
printf("enter the fathers ID\n");
scanf("%d", &((*pdata)[i].father.id));
in the loop.
Fixing the pointers may have solved your problem. But the program has a lot of duplicate code and rewriting as follows would help you test a small portion and debug the program easily.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 100
typedef struct person {
int id;
char *firstName;
int age;
} person;
typedef struct family {
char *lastName;
person father, mother;
person *children;
int numChildren;
} family;
void input_string(const char *prompt, char **where) {
char temp[SIZE];
printf("%s\n", prompt);
scanf("%s", temp);
*where = malloc(sizeof(char) * (strlen(temp) + 1));
strcpy(*where, temp);
}
void input_int(const char *prompt, int *where) {
printf("%s\n", prompt);
scanf("%d", where);
}
void input_person(const char *name, person *person) {
char prompt[SIZE];
sprintf(prompt, "Enter the %s's first name", name);
input_string(prompt, &person->firstName);
sprintf(prompt, "Enter the %s's ID", name);
input_int(prompt, &person->id);
sprintf(prompt, "Enter the %s's age", name);
input_int(prompt, &person->age);
}
void input_family(family *fam) {
input_string("Please enter the last name", &fam->lastName);
input_person("father", &fam->father);
input_person("mother", &fam->mother);
input_int("Please enter the number of children", &fam->numChildren);
fam->children = malloc(sizeof(person) * (fam->numChildren));
for (int i = 0; i < fam->numChildren; i++) {
input_person("kid", &(fam->children)[i]);
}
}
int initializeHouse(family **families) {
int size;
input_int("Please enter the number of families", &size);
*families = malloc(sizeof(family) * size);
for (int i = 0; i < size; i++) {
input_family(&(*families)[i]);
}
return size;
}
int main() {
int size = 0;
family *a;
size = initializeHouse(&a);
printf("Successfully inputted %d families", size);
return 0;
}
I am getting garbage value when I display the records.
I have to create a database of students in C using array of structures and without pointers.
Is there any other way of doing this?
How to use array of structures?
#include <stdio.h>
struct student {
char first_name[10],last_name[10];
int roll;
char address[20];
float marks;
};
void accept(struct student);
void display(struct student);
void main() {
struct student S[10];
int n, i;
printf("Enter the number of records to enter : ");
scanf("%d", &n);
for (i = 0; i < n; i++) {
accept(S[i]);
}
for (i = 0; i < n; i++) {
display(S[i]);
}
}
void accept(struct student S) {
scanf("%s", S.first_name);
scanf("%s", S.last_name);
scanf("%d", &S.roll);
scanf("%s", S.address);
scanf("%f", &S.marks);
}
void display(struct student S) {
printf("\n%s", S.first_name);
printf("\n%s", S.last_name);
printf("\n%d", S.roll);
printf("\n%s", S.address);
}
Everything in C is pass-by-value. Which means you are modifying variable copy in stack frame, while real variable passed as parameter remains untouched.
You have to pass an pointer to variable which you want to modify in function.
// Function declaration
void accept(struct student *);
// Call
accept(&S[i]);
// Usage in function via dereference operator
scanf("%s",S->first_name);
If you would like to enter unknown amount of records, you should use VLA (since c99) or dynamically allocate structures.
VLA
scanf("%d",&n);
struct student S[n];
Dynamic callocation
scanf("%d",&n);
struct student * S = malloc(sizeof(struct student) * n);
Because in your case, if user input more that 9 records you are touching outside of bounds, which has undefined behavior.
There are multiple issues in your code:
The standard prototype for main without arguments is int main(void)
You should allocate the array dynamically with calloc.
you should pass structure pointers to the accept and display functions instead of passing structures by value. Passing the destination structure by value is incorrect as the accept function cannot modify the structure in the main function, which remains uninitialized and causes garbage to be displayed. Note that it is actually undefined behavior to access uninitialized data so the program could behave in even worse ways.
You should provide scanf() with the maximum number of arguments to store into character arrays to avoid potential buffer overflows.
you should verify the return values of scanf() to avoid undefined behavior on invalid input.
you could use the %[^\n] scan set to allow embedded spaces in the address field.
Here is a modified version:
#include <stdio.h>
#include <stdlib.h>
struct student {
char first_name[10], last_name[10];
int roll;
char address[20];
float marks;
};
void accept(struct student *sp);
void display(const struct student *sp);
int main(void) {
struct student *S;
int n, i, j;
printf("Enter the number of records to enter : ");
if (scanf("%d", &n) != 1)
return 1;
S = calloc(sizeof(*S), n);
if (S == NULL) {
return 1;
}
for (i = 0; i < n; i++) {
accept(&S[i]);
}
for (i = 0; i < n; i++) {
display(&S[i]);
}
free(S);
return 0;
}
void accept(struct student *sp) {
if (scanf("%9s%9s&d %19[^\n]%f",
sp->first_name, sp->last_name, &sp->roll,
sp->address, &sp->marks) != 5) {
printf("missing input\n");
exit(1);
}
}
void display(const struct student *sp) {
printf("%s\n", sp->first_name);
printf("%s\n", sp->last_name);
printf("%d\n", sp->roll);
printf("%s\n", sp->address);
printf("%f\n", sp->marks);
printf("\n");
}
I have an issue with my code, I changed a few of the functions to accomodate the structure I added, so instead of having variables all over the place, but now it does not work at all. I need it to create a structure person, then it prompts the user to enter the persons name, and age; then it asks for more persons to fill a doubly linked list which stops the loop if nothing is input for the persons name. THEN it spits out the reverse of what I input into the doubly linked list. All help is appreciated ^-^
struct person
{
char name[10][41];
int age[10];
};
int write(struct person *people);
void print(struct person *people);
int main(void)
{
char names[10][41];
int n = 10;
int ages[10];
typedef struct person people;
n = write(people);
print(people);
system("PAUSE");
return 0;
}
int write(struct person *people)
{
int i;
char name[41];
int age[10];
for(i=0; i<=i; i++)
{
fflush(stdin);
printf("Enter full name\n");
gets(people.name);
strcpy(names[i], name);
if(names[i][0] == '\0')
break;
printf("Enter their age\n");
scanf("%d", &age[i]);
ages[i] = age[i];
}
}
void print(struct person *people)
{
int i = 0;
for(i = 0; i < 10; i++)
{
if(names[i][0] == '\0')
break;
printf("%s is %d year(s) old\n", names[i], ages[i]);
}
return i;
}
You are passing the name of a type that you just defined instead of a variable declared of that type, this
typedef struct person people;
should be
struct person people;
Change
n = write(people);
to
n = write(&people);
Remove fflush(stdin) it's undefined behavior.
Do not use gets() it's very unsafe, use fgets() instead
char name[40];
gets(name);
should be
char name[40];
fgets(name, sizeof(name), stdin);
I have come across this wierd and mysterous (at least to me) error that I am finding a very hard time finding. It gives me an error at the line where I call my function input(student_list1[MAX], &total_entries); where the compiler says:
incompatible type for agument 1 in 'input'
What am I doing wrong here? I sense it something very simple and stupid but I have gone through the code several times now without any avail.
#define MAX 10
#define NAME_LEN 15
struct person {
char name[NAME_LEN+1];
int age;
};
void input(struct person student_list1[MAX], int *total_entries);
int main(void)
{
struct person student_list1[MAX];
int total_entries=0, i;
input(student_list1[MAX], &total_entries);
for(i=0; i<total_entries; i++)
{
printf("Student 1:\tNamn: %s.\tAge: %s.\n", student_list1[i].name, student_list1[i].age);
}
return 0;
} //main end
void input(struct person student_list1[MAX], int *total_entries)
{
int done=0;
while(done!=1)
{
int i=0;
printf("Name of student: ");
fgets(student_list1[i].name, strlen(student_list1[i].name), stdin);
student_list1[i].name[strlen(student_list1[i].name)-1]=0;
if(student_list1[i].name==0) {
done=1;
}
else {
printf("Age of student: ");
scanf("%d", student_list1[i].age);
*total_entries++;
i++;
}
}
}
struct person student_list1[MAX] in the function argument is actually a pointer to struct person student_list1.
student_list1[MAX] you passed is a (out of bound) member of the array struct person student_list1[MAX]. Valid array index shoudl be between 0 to MAX - 1.
Change it to:
input(student_list1, &total_entries);
Note that here the array name student_list1 is automatically converted to a pointer to student_list1[0].
There are many things wrong with the code; this is my attempt at making it somewhat more robust:
#include <stdio.h>
#include <string.h>
#define MAX 10
#define NAME_LEN 15
// use a typedef to simplify code
typedef struct person {
char name[NAME_LEN];
int age;
} person_t;
// size qualifier on student_list is redundent and person_t* does the same
void input(person_t *student_list, int *total_entries);
int main(void)
{
person_t student_list[MAX];
int total_entries, i;
// pass array and not the non-existent 'student_list[MAX]' element
input(student_list, &total_entries);
for(i=0; i<total_entries; i++)
{
// age is an int, not a string so use %d
printf("Student 1:\tName: %s.\tAge: %d.\n", student_list[i].name, student_list[i].age);
}
return 0;
} //main end
void input(person_t *student_list, int *total_entries)
{
int done = 0, i = 0;
*total_entries = 0;
while (i < MAX) {
printf("Name of student: ");
// use NAME_LEN instead of strlen(list[i].name) because latter is
// probably not initialized at this stage
if (fgets(student_list[i].name, NAME_LEN, stdin) == NULL) {
return;
}
// detect zero-length string
if (student_list[i].name[0] == '\n') {
return;
}
printf("Age of student: ");
scanf("%d", &student_list[i].age);
// read the newline
fgetc(stdin);
*total_entries = ++i;
}
}
input(student_list1[MAX], &total_entries); shoud be input(student_list1, &total_entries);.
In C,
void input(struct person student_list1[MAX], int *total_entries);
equals
void input(struct person *student_list1, int *total_entries);