Releasing pointer memory aswell as pointer itself - c

A "Deeltal" keeps track of how many dividers an integer has (count) and keeps them in an array (dividers).
Examples:
value = 8 -> count = 3 and dividers = {1,2,4}
value = 10, count = 3, dividers = {1,2,5}
Hope everything is clear, take a look at the following code:
typedef struct{
int value;
int count;
int* dividers;
} Deeltal;
void free_dividers(Deeltal *g){ /*Deletes the int* dividers of a given Deeltal*/
free (g - > dividers);
}
/* the following two functions have the same purpose: deleting the content of a
given amount of "Deeltal" AND deleting the pointer to it aswell*/
void free_amountOfdeeltal(Deeltal *d, int amount){
int i;
for (i = 0; i < amount; i++){
free_dividers(&d[i]);
}
free(d);
}
void free_amountOfdeeltalVersion2(Deeltal **g, int amount){
int i;
for(i = 0; i < amount; i++){
free_dividers(&(*g)[i]);
}
free(*g);
}
If my main looked something like this
int main(void){
/*EDIT 3/11/2017: forgot to allocate memory for *d and initializing g.
Thanks for pointing this out*/
Deeltal g = 0;
g.value = 6; g.count = 3; g.dividers = {1,2,3};
Deeltal *d = malloc(sizeof(Deeltal));
d->value = 6; d->count = 3; d->dividers = {1,2,3};
free_amountOfdeeltal(&g);
free_amountOfdeeltalVersion2(&d);
}
What is the difference between free_amountOfdeeltal and free_amountOfdeeltalVersion2?
Both should do the same thing: releasing the memory of a Deeltal and also deleting the pointer pointing to that memory.
On a sidenote:
How do you delete the memory as well as the pointer?

Not withstanding calling this function with invalid data as pointed out by others .. I'll attempt to answer the question I think you are asking.
On a sidenote: How do you delete the memory as well as the pointer?
You can't really "delete the pointer" in this context as a pointer is simply a variable that is assigned an address. You delete memory that was allocated to you by passing free a pointer to the memory. Note that free does not modify the value of the pointer at all. (It can't because the pointer is passed by value.) After the call to free the pointer still points to the same memory address.
If what you mean is "how can I assign a meaningful value to the pointer to identify that its memory has already been deleted," then you can use the second form of your function:
void free_amountOfdeeltalVersion2(Deeltal **g, int amount);
and set *g to NULL before returning. You can then use this information than the pointer is NULL to identify the memory has already been deleted.

You didn't allocate any memory for d so your pointer doesn't point to any structure. Therefor, you can't access its properties or free its memory because you didn't reserve it in the first place. There's no way this code could come remotely close to compiling.
First of all you should be allocating memory for a "Deeltal" structure like this:
Deeltal *d = malloc(sizeof(Deeltal));
I recommend you go back and relearn how pointers work, as you're doing some really weird stuff there.

Related

Memory leak in C Program

I have made a C program in which I have used structures defined as:
typedef struct Move{
int from_x;
int from_y;
int to_x;
int to_y;
int piece;
}Move;
typedef struct ListofMove{
Move* array;
int len;
}ListofMove;
typedef struct Board{
int B[8][8];
double value;
double value_w;
double value_b;
int material_w;
int material_b;
int mobility_w;
int mobility_b;
int dev_w;
int dev_b;
int center_w;
int center_b;
int devArr[4][8];
int side;
ListofMove moves_w;
ListofMove moves_b;
struct Board* children_w;
struct Board* children_b;
int len_w;
int len_b;
struct Board *parent;
double alpha;
double beta;
}Board;
The data in ListofMove and Board* children_w and children_b are added using realloc() function.The main() contains only a single function call for some iterations (here let us say 30)
int main(){
double BW[4] = {5.689821, 39.038832, 26.088224, 60.491498};
double WW[4] = {82.091284, 83.026237, 46.478279, 49.979957};
int outres, in;
for(in = 0 ; in<20; in++){
depth = 0; Nply = 0; count = 0;
outres = gameplay(BW, WW);
}
return 0;
}
All the variables are declared locally in the function gameplay() and are used further by other function call made in gameplay(either by call by value or call by address). Once used all the variables are explicitly deleted using the function del(Board* b) and delm(Move* m).
int gameplay(double blwght[], double whwght[]){
int i, ind;
Board pre;
Board result;
Board current;
Move cur_B, cur_W;
.............
..............
.......
del(&pre);
del(&result);
del(&current);
delm(&cur_B);
delm(&cur_W);
}
The definition for deleting functions
void del(Board* b){
b->beta = 0;
b->alpha = 0;
b->material_w = 0;
b->material_b = 0;
b->mobility_w = 0;
b->mobility_b = 0;
b->center_w = 0;
b->center_b = 0;
b->dev_w = 0;
b->dev_b = 0;
b->value_w = 0;
b->value_b = 0;
b->value = 0;
b->side = 0;
free(&b->value_w);
free(&b->value_b);
free(&b->center_w);
free(&b->center_b);
free(&b->dev_w);
free(&b->dev_b);
free(&b->mobility_w);
free(&b->mobility_b);
free(&b->material_w);
free(&b->material_b);
free(&b->side);
free(&b->len_w);
free(&b->len_b);
free(&b->alpha);
free(&b->beta);
free(b->B);
free(b->devArr);
free(b->parent);
ClearWBoardList(b);
ClearBBoardList(b);
ClearMoveList(&b->moves_w);
ClearMoveList(&b->moves_b);
free(&b->moves_w.array);
free(&b->moves_b.array);
free(&b->moves_w);
free(&b->moves_b);
}
void delm(Move* m){
m->from_x = 0;
m->from_y = 0;
m->to_x = 0;
m->to_y = 0;
m->piece = 0;
free(&m->from_x);
free(&m->from_y);
free(&m->to_x);
free(&m->to_y);
free(&m->piece);
}
The problem is even after the variables are deleted and the function call is executed completely for few iterations the program crashes (after about 14 iteration in my case where system has a 3GB RAM). the problem detected was that before crashing it used about 2GB memory as memory used in one function call is not freed after its execution completes. Can anyone Pls suggest by the memory is retained by variables even after function call returned the value and even when they are explicitly deleted and any solution to solve this problem.
As per the formatting of your question, its too hard to understand the problem, but at first look, it seems, you're passing non-malloced pointers to free() . The result is undefined behaviour.
Please remove
free(&b->value_w);
free(&m->from_x);
and the remaining compile-time allocated variable addresses.
As per the rules, free()-ing is only allowed [rather, required] for dynamically allocated memory. OTOH, Compile-time memory need not to be freed explicitly from your program.
Related Reading: According to Chapter 7.20.3.2, C99 standard, paragraph 2
The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by the calloc, malloc, or realloc function, or if the space has been deallocated by a call to free or realloc, the behavior is undefined.
Also, you should refer to the manual page for free().
Other than this, for the leak in your case, you're freeing the b->parent but did not free the nested allocated memory for b->parent. Again, you did not free children_w and children_b at all. They all need to be taken care properly.
In your void del(Board* b)() function, you freeing free(b->parent); which is a linked list but you have two more linked lists struct Board* children_w; and struct Board* children_b; which also needs to be freed properly.
In Linked lists, you have to reach to and delete each node explicitly using free().
take a look at this aspect in your code. It is not clear from code above about these linked lists.
Sourav is correct you don't free the parameters of Board unless u explicitly allocated memory for them, otherwise it result in undesirable effects (you may be freeing random memory and leaving dangling pointers in memory). I suggest u run Valgrind: valgrind --leak-check=yes myprog arg1 arg2 and read http://valgrind.org/docs/manual/quick-start.html for more infomation

Freeing array of struct

I've done some research and couldn't find any answer to my problem.
I'm having problems with freeing my struct.
This is how i create my struct:
struct Structure * newStructure(int N)
{
struct Structure * structure;
int i;
structure = (struct Structure * ) malloc(N * sizeof(struct Structure));
for (i = 0; i < N; i++)
{
structure[i].i_Number = (int * ) malloc(sizeof(int));
structure[i].c_Char = (char * ) malloc(sizeof(char));
structure[i].c_Char[0] = '\0';
structure[i].d_Float = (double * ) malloc(sizeof(double));
}
return structure;
}
Everything works to this point. Later I fill every variable with random values so that they are not empty.
I call my freeMemory function like this freeMemory(structure, amountOfStructures);
And here is freeMemory function itself:
void freeMemory (struct Structure* structure, int N)
{
int i;
for( i=0 ; i<N ; i++ )
{
if (structure[i].i_Number!=NULL) free(structure[i].i_Number);
if (structure[i].c_Char!=NULL) free(structure[i].c_Char);
if (structure[i].d_Float!=NULL) free(structure[i].d_Float);
}
free(structure);
}
The free(structure) part works fine. But there are problems with the for loop and I have no idea what I'm doing wrong here.
#EDIT
I'm adding my struct declaration:
struct Structure{
int *i_Number;
char *c_Char;
double *d_Float;
};
#EDIT2
That's the function that initializes struct:
struct Structure* randomizing (int N)
{
struct Structure* structure = newStructure(N); int i;
srand(time(NULL));
for (i = 0; i < N; i++)
{
int _i; char _c; double _d;
_i = rand()%1000000;
_c = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" [rand () % 26];
_d = 0;
setStructureNumber(structure, i,(int*) _i);
setStructureChar(structure, i, (char*) _c);
setStructureDouble(structure, i, &_d);
// I'VE COMMENTED OUT THE MUTATORS ABOVE AND THE ERROR DOES NOT SHOW ANYMORE, SO THERES SOMETHING WRONG WITH THEM
}
return structure;
}
And im calling it like this:
struct Structure* structure;
structure = randomizing(amountOfStructures);
The mutators used:
// Mutators
void setStructureNumber (struct Structure* structure, int p, int* num)
{
if (structure[p].i_Number != NULL) free(structure[p].i_Number);
structure[p].i_Number = (int*) malloc (sizeof(int));
structure[p].i_Number = num;
}
void setStructureChar (struct Structure* structure, int p, char* str)
{
if (structure[p].c_Char != NULL) free(structure[p].c_Char);
structure[p].c_Char = (char*) malloc (sizeof(char));
structure[p].c_Char = str;
}
void setStructureDouble (struct Structure* structure, int p, double* dou)
{
if (structure[p].d_Float != NULL) free(structure[p].d_Float);
structure[p].d_Float = (double*) malloc (sizeof(double));
structure[p].d_Float = dou;
}
The most likely reason is that somewhere in your code you go out of bounds of the memory you allocated and thus destroy the integrity of the heap. A frequently encountered practical manifestation of such undefined behavior is a failure at free, when the library detects the problem with the heap.
Inside you allocation cycle you allocate just one object of each respective type for each field of your struct object. For example, you allocate only one character for c_Char field and initialize it with \0. This might suggest that c_Char is intended to hold a string (is it?). If so, then the memory you allocated is sufficient for an empty string only. If you do not reallocate that memory later, any attempts to place a longer string into that memory will break the integrity of the heap and trigger undefined behavior.
The same applies to other fields as well. However, without extra explanations from you it is not possible to say whether it is right or wrong. At least, you have to provide the definition of struct Structure. And you have to explain your intent. Why are you dynamically allocating single-object memory for struct fields instead of just making these objects immediate members of the struct?
The additional code you posted is completely and utterly broken.
Firstly you are calling your mutators as
setStructureNumber(structure, i,(int*) _i);
setStructureChar(structure, i, (char*) _c);
setStructureDouble(structure, i, &_d);
This does not make any sense. Why are you trying to convert integer value _i to pointer type??? If you want to obtain a pointer to _i, it is done as &_i. You already do it correctly in the very last call, where you pass &_d. Why are the first two calls different from the last one? What was your logic behind this?
Secondly, inside your mutator functions
void setStructureNumber (struct Structure* structure, int p, int* num)
{
if (structure[p].i_Number != NULL) free(structure[p].i_Number);
structure[p].i_Number = (int*) malloc (sizeof(int));
structure[p].i_Number = num;
}
you are freeing old memory and allocating new memory. Why? Why don't just reuse the old memory to store the new value? (BTW, there's no need to check the pointer for null before calling free, because free will check it internally anyway.)
Thirdly, after allocating the new memory you immediately leak it by overriding the pointer value returned by malloc with the pointer value passed from the outside
structure[p].i_Number = num;
Again, this does not make any sense. This is actually what causes the crash on free - the pointers you pass from the outside are either meaningless random values (like your (int *) _i or (char *) _c)) or point to a local variable (like your &_d).
There's no way to "correct" your code without knowing what it is you are trying to do in the first place. There are just too many completely unnecessary memory allocations and reallocations and other illogical things. I would simply rewrite the mutator functions as
void setStructureNumber (struct Structure* structure, int p, int num)
{
*structure[p].i_Number = num;
}
Note - no memory reallocations and the argument is passed by value.
The functions would be called as
setStructureNumber(structure, i, _i);
setStructureChar(structure, i, _c);
setStructureDouble(structure, i, _d);
But again, this is so vastly different from what you have that I don't know whether this is what you need.
Technically, there is nothing wrong with what you are doing (except the missing error checks on allocations, unnecessary casts of malloc results, and unnecessary NULL checking before calling free).
This should work fine, assuming that you pass the correct value of N, and that you do not free things more than once:
struct Structure * newStructure(int N) {
struct Structure * structure = malloc(N * sizeof(struct Structure));
for (int i = 0; i < N; i++) {
structure[i].i_Number = malloc(sizeof(int));
structure[i].c_Char = malloc(sizeof(char));
structure[i].c_Char[0] = '\0';
structure[i].d_Float = malloc(sizeof(double));
}
return structure;
}
void freeMemory (struct Structure* structure, int N)
{
for(int i=0 ; i<N ; i++ )
{
free(structure[i].i_Number);
free(structure[i].c_Char);
free(structure[i].d_Float);
}
free(structure);
}
You can use a memory diagnostic tool such as valgrind to ensure that you do not freeing things more than once.
In your mutators you leak memory and then point to local variables (comments mine)
void setStructureChar (struct Structure* structure, int p, char* str)
{
if (structure[p].c_Char != NULL) free(structure[p].c_Char);
// allocates new memory and points c_Char at it.
structure[p].c_Char = (char*) malloc (sizeof(char));
// makes c_Char point to where `str` is pointing; now the allocated memory is leaked
structure[p].c_Char = str;
}
When you later do free on structure[p].c_Char, it causes undefined behaviour because you called this function with a pointer to a local variable. You probably have undefined behaviour elsewhere too if you try to access c_Char anywhere before freeing it.
The other mutators have the same problem.
To "fix" this change structure[p].c_Char = str; to *structure[p].c_Char = *str;.
You also have blunders here:
setStructureNumber(structure, i,(int*) _i);
setStructureChar(structure, i, (char*) _c);
You meant &_i and &_c respectively. I would advise to remove all casts from your code. At best they are redundant; at worst (e.g. in these two lines) they hide an error which the compiler would diagnose.
Also remove all the NULL checks before free, they are redundant and make your code hard to read. Instead, do the NULL checks after calling malloc, and abort the program if malloc returned NULL.
However this whole setup seems like a ghastly design. You could pass the things by value to the mutators. And you could change your struct to not contain pointers, and therefore not need all this extra allocation.

Cannot return int array

I want to use only studio.h library to convert from decimal number to binary number by using an array to store remainder but the result is not correct, maybe i have problem with memory allocation or return value is wrong, please help me to check it.
Thank you so much!
#include <stdio.h>
int n = 0;
int* DecimalToBinary(int number){
int a[10];
while(number!=0){
a[n++] = number%2;
number/=2;
}
return a;
}
void main(){
int *d1 = DecimalToBinary(5);
int *d2 = DecimalToBinary(10);
for(int i = n-1 ;i>=0;i--)
printf(" %d",d1[i]);
printf("\n");
for(int i = n-1 ;i>=0;i--)
printf(" %d",d2[i]);
}
You return a pointer to a local array. That local array is on the stack, and when the function returns the array goes out of scope and that stack memory will be reused when you call the next function. This means that the pointer will now point to some other data, and not the original array.
There are two solutions to this:
Declare the array in the function calling DecimalToBinary and pass it as an argument.
Create the array dynamically on the heap (e.g. with malloc) and return that pointer.
The problem with method 2 is that it might create a memory leak if you don't free the returned pointer.
As noted by Craig there is a third solution, to make the array static inside the function. However in this case it brings other and bigger problems than the two solutions I originally listed, and that's why I didn't list it.
There is also another serious problem with the code, as noted by Uchia Itachi, and that is that the array is indexed by a global variable. If the DecimalToBinary function is called with a too big number, or to many times, this global index variable will be to big for the array and will be out of bounds for the array.
Both the problem with dereferencing a pointer to an out-of-scope array and the indexing out of bounds leads to undefined behavior. Undefined behavior will, if you're lucky, just lead to the wrong result being printed. If you're unlucky it will cause the program to crash.
You are returning a pointer to a locally allocated array. It is allocated on the stack, and goes away when the function returns, leaving your pointer pointing to garbage.
You have a few options. You could pass an array in to fill:
void DecimalToBinary(int result[10],int number){
while(number!=0){
result[n++] = number%2;
number/=2;
}
return result;
}
// usage example:
int b[10];
DecimalToBinary(b, 42);
Or you could allocate an array on the heap:
int* DecimalToBinary(int number){
int *a = (int *)malloc(sizeof(int) * 10);
while(number!=0){
a[n++] = number%2;
number/=2;
}
return a;
}
// usage example
int *b = DecimalToBinary(42);
free(b); // when finished with it
Or you could wrap the array in a struct:
typedef struct {
int b[10];
} result;
result DecimalToBinary(int number){
result r;
while(number!=0){
r.b[n++] = number%2;
number/=2;
}
return r;
}
// usage example
result r = DecimalToBinary(42);
If you do the malloc() option, do not forget to free() the returned data when you're done with it, otherwise it will hang around. This is called a memory leak. In more complex programs, it can lead to serious issues.
Note: By the way, if your number is larger than 1023 (10 binary digits), you'll overrun the array. You may also wish to explicitly stop once you've stored 10 digits, or pass the size of the array in, or compute the required size first and allocate that much space. Also, you will get some odd results if your number is negative, you might want to use number&1 instead of number%2.
Note 2: As noted elsewhere, you should make n local, or at the very least reinitalize it to 0 each time the function is called, otherwise it will just accumulate and eventually you'll go past the end of the array.
int[10] is not the same as int *; not only is the former created on the stack, it is a different type alltogether. You need to create an actual int * like so:
int *a = malloc (10 * sizeof (int));
Of course, don't forget to free() it after use!
What you can also do and what is commonly done in C is creating the array where it is called and provide a pointer to that array to the function, this way when the array is on the stack of the function that calls it and not in the function self. We also have to specify the size of the array on to that function, since the function cannot know to how many elements the pointer points to
void DecimalToBinary( int number, int* output, unsigned size ) {
/*adapt this to your liking*/
int i;
for ( i = 0; i < size && number != 0; i++) {
output[i] = number%2;
number/2;
}
}
and in you main function you would call it like this:
int array[10];
DecimalToBinary( 5, array, sizeof(array)/sizeof(array[0]));
now array has the same result as a would have had in your example.
The problem in your code lies here..
int * DecimalToBinary(int number){
int a[10];
while(number!=0){
a[n++] = number%2;
number/=2;
}
return a;
}
The array a scope is only till this function. Once this function terminates, the memory allocated for this array will be released, either u need to use dynamic memory allocation or make array a global.
This is the correct program:
#include <stdio.h>
int n = 0;
int a[10] = {0};
int* DecimalToBinary(int number){
n = 0;
while(number!=0){
a[n++] = number%2;
number = number/2;
}
return a;
}
int main(){
int *d1;
int *d2;
int i;
d1 = DecimalToBinary(5);
for(i = n-1;i>=0;i--)
printf(" %d",d1[i]);
printf("\n");
d2 = DecimalToBinary(10);
for(i = n-1;i>=0;i--)
printf(" %d",d2[i]);
printf("\n");
}

C using malloc and duplicating array

I am supposed to follow the following criteria:
Implement function answer4 (pointer parameter and n):
Prepare an array of student_record using malloc() of n items.
Duplicate the student record from the parameter to the array n
times.
Return the array.
And I came with the code below, but it's obviously not correct. What's the correct way to implement this?
student_record *answer4(student_record* p, unsigned int n)
{
int i;
student_record* q = malloc(sizeof(student_record)*n);
for(i = 0; i < n ; i++){
q[i] = p[i];
}
free(q);
return q;
};
p = malloc(sizeof(student_record)*n);
This is problematic: you're overwriting the p input argument, so you can't reference the data you were handed after that line.
Which means that your inner loop reads initialized data.
This:
return a;
is problematic too - it would return a pointer to a local variable, and that's not good - that pointer becomes invalid as soon as the function returns.
What you need is something like:
student_record* ret = malloc(...);
for (int i=...) {
// copy p[i] to ret[i]
}
return ret;
1) You reassigned p, the array you were suppose to copy, by calling malloc().
2) You can't return the address of a local stack variable (a). Change a to a pointer, malloc it to the size of p, and copy p into. Malloc'd memory is heap memory, and so you can return such an address.
a[] is a local automatic array. Once you return from the function, it is erased from memory, so the calling function can't use the array you returned.
What you probably wanted to do is to malloc a new array (ie, not p), into which you should assign the duplicates and return its values w/o freeing the malloced memory.
Try to use better names, it might help in avoiding the obvious mix-up errors you have in your code.
For instance, start the function with:
student_record * answer4(const student_record *template, size_t n)
{
...
}
It also makes the code clearer. Note that I added const to make it clearer that the first argument is input-only, and made the type of the second one size_t which is good when dealing with "counts" and sizes of things.
The code in this question is evolving quite quickly but at the time of this answer it contains these two lines:
free(q);
return q;
This is guaranteed to be wrong - after the call to free its argument points to invalid memory and anything could happen subsequently upon using the value of q. i.e. you're returning an invalid pointer. Since you're returning q, don't free it yet! It becomes a "caller-owned" variable and it becomes the caller's responsibility to free it.
student_record* answer4(student_record* p, unsigned int n)
{
uint8_t *data, *pos;
size_t size = sizeof(student_record);
data = malloc(size*n);
pos = data;
for(unsigned int i = 0; i < n ; i++, pos=&pos[size])
memcpy(pos,p,size);
return (student_record *)data;
};
You may do like this.
This compiles and, I think, does what you want:
student_record *answer4(const student_record *const p, const unsigned int n)
{
unsigned int i;
student_record *const a = malloc(sizeof(student_record)*n);
for(i = 0; i < n; ++i)
{
a[i] = p[i];
}
return a;
};
Several points:
The existing array is identified as p. You want to copy from it. You probably do not want to free it (to free it is probably the caller's job).
The new array is a. You want to copy to it. The function cannot free it, because the caller will need it. Therefore, the caller must take the responsibility to free it, once the caller has done with it.
The array has n elements, indexed 0 through n-1. The usual way to express the upper bound on the index thus is i < n.
The consts I have added are not required, but well-written code will probably include them.
Altought, there are previous GOOD answers to this question, I couldn't avoid added my own. Since I got pascal programming in Collegue, I am used to do this, in C related programming languages:
void* AnyFunction(int AnyParameter)
{
void* Result = NULL;
DoSomethingWith(Result);
return Result;
}
This, helps me to easy debug, and avoid bugs like the one mention by #ysap, related to pointers.
Something important to remember, is that the question mention to return a SINGLE pointer, this a common caveat, because a pointer, can be used to address a single item, or a consecutive array !!!
This question suggests to use an array as A CONCEPT, with pointers, NOT USING ARRAY SYNTAX.
// returns a single pointer to an array:
student_record* answer4(student_record* student, unsigned int n)
{
// empty result variable for this function:
student_record* Result = NULL;
// the result will allocate a conceptual array, even if it is a single pointer:
student_record* Result = malloc(sizeof(student_record)*n);
// a copy of the destination result, will move for each item
student_record* dest = Result;
int i;
for(i = 0; i < n ; i++){
// copy contents, not address:
*dest = *student;
// move to next item of "Result"
dest++;
}
// the data referenced by "Result", was changed using "dest"
return Result;
} // student_record* answer4(...)
Check that, there is not subscript operator here, because of addressing with pointers.
Please, don't start a pascal v.s. c flame war, this is just a suggestion.

Comparison of pointer to integer errors in standard C

I'm changing my code from variable to pointers and I'm having a bit of trouble. Where it used to work with (largely abbreviated):
int best = 0;
int max = 10;
if (max > best) {
best = max;
}
I'm trying to use pointers so that I can use pass-by reference to abstract it into a function.
int *best;
*best = 0;
int max = 10;
if (max > *best) {
*best = max;
}
I get segmentation faults at the (max > *best) line. Can you tell me where I'm going wrong?
I don't know how it got even that far because of:
int *best;
*best = 0;
You are simply grabbing 4 bytes which have some (unknown to you) previous value, interpreting that as a memory location and writing all zeroes on it.
Longer explanation: int *best gives you use of the name best to refer to a memory location. Trouble is, you have not specified which memory location you want. Since a pointer is nothing more than a number of bytes in memory, and those bytes hold some value (even unused memory holds some value), in effect your new pointer is pointing to an unknown memory location. When you dereference it, bad things happen.
Try it this way:
int someInt = 0;
int* best = &someInt;
*best = 0;
Now you know what memory you are overwriting with zeroes: the piece that was properly reserved for the variable someInt.
In the second example, your best isn't being initialized, thus it will point to an unknown address. You may want to point it to an existing int. For example:
int best = 0;
int *best_ptr = &best; // Now best_ptr points to best
printf("value is %d\n", *best_ptr);
Or maybe allocate memory for it instead:
int *best_ptr = malloc(sizeof(int)); // Allocate
if (best_ptr != NULL) {
*best_ptr = 0;
printf("value is %d\n", *best_ptr);
free(best_ptr); // Deallocate
}
you're assigning an address to the pointer, not a value. Change it to this:
int* pbest;
int best;
pbest = &best;
*pbest = 0;
int max = 10;
if (max > *best) {
*best = max;
}
i think the problem is that you can't assign a integer to a pointer
instead , you should assign a position to a pointer like
int score;
int *best = &score;
and then you can assign an integer to socre
score = 0;

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