Questions tagged [malloc]
59
questions
3
votes
1answer
13k views
How to free a nested struct?
In preparation for my final project, I am writing a C program that handles task lists. It utilizes a nested struct. For every line it reads from a file it creates a struct of type task. Each task then ...
2
votes
1answer
2k views
Pointers and arrays, don't understand the relationship
I made two structs, they are very similar. The first one is a node and the second one, called hash, only contains a pointer to a node. In main I've made pointers to allocated memory for them. newNode ...
2
votes
1answer
81 views
pset2/crack/(Memory issue)
If I run this code for the first time it gives me the desired output. But on the second run, I don't get the desired output. It seems like memory is not given free.
#include <stdio.h>
#include &...
1
vote
1answer
190 views
segfault while freeing memory in speller
I'm having an enormous problem implementing the unload function for the speller in pset6. Although it's not a well-polished algorithm I first wanted to make a quick design that allows me to take a ...
1
vote
1answer
560 views
Recursion Destroy Singly linked List, memory leak?
I'm working through some personal test code to make sure I understand how to work withs singly linked lists.
I'm basically going through the Week 5 Section video on singly linked lists and putting ...
1
vote
2answers
597 views
declaring char array vs malloc
I was watching the week 5 lecture and David said that a chunk of memory can be allocated two ways:
using malloc();
declaring an array of a certain size (char buffer[10]).
Is there really any ...
1
vote
1answer
407 views
malloc an array - hash table - Pset 6
Initially i had no problems implementing my hash table during the load function.
however when it came time to check for errors, i couldn't access my hash table in order to traverse my linked list.
I ...
1
vote
1answer
36 views
spellchecker unload not freeing 1 block
What is not freeing!?
[code snipped by mod]
// end of load function (mod comment)
return true;
fclose(dict_file);
}
[code snipped by mod]
0
votes
1answer
6k views
Invalid pointer error when using free()
I was trying to practice malloc'ing and freeing memory, however when I run the free() function in this program an error is returned for an invalid pointer. Can anyone tell me what I'm doing wrong?
...
0
votes
1answer
133 views
problem with recover.c using malloc and fread
i tried to write a function that sample 4 bytes from card.raw file but i doesn't work because fread doesn't put any data into block buffer so i wrote this simple code and i found out that fgetc works ...
0
votes
1answer
207 views
pset4 recover with malloc having a segmentation fault
I can't seem to find the reason of why I'm getting the segmentation fault in my code. The moment my code starts to write the bytes of buffer, I encounter the fault
Any help is really appreciated.
#...
0
votes
2answers
295 views
Pset5 - Problem with hash table load(), malloc, and segmentation-fault
I am having problem with the load function. When I run:
valgrind --leak-check=full ./speller texts/austinpowers.txt
it gives me the following report (I am using the small dictionary to test my code) ...
0
votes
3answers
127 views
Week 4, Section : Dynamic Memory Allocation
After watching Dynamic Memory allocation section
and reading this i am a bit confused,
if declaring an array
int array[10];
and allocating using malloc int* parray = malloc(10 * sizeof(int));...
0
votes
2answers
239 views
Segmentation fault in recover.c (pset4)
On checking with valgrind, I get main (recover.c:89)
==14182== Address 0x55022c8 is 0 bytes after a block of size 8 alloc'd
There are 2 more problems with malloc again, while doing sprintf and ...
0
votes
1answer
132 views
Want to make sure I understand struct, malloc, and pointers and how they relate to each other
Sort of related to PSET4 resize, but actually want to make sure I understand this in general.
So at first I just declared a struct BITMAPINFOHEADER called "new_bi" and dealt with it while avoiding ...
0
votes
1answer
451 views
fread not putting what I expect in buffer
for Pset4, recover, I'm trying to read 4 bytes from card.raw into a buffer. I''m testing the first 4 bytes of card.raw with what my buffer contains using gdb, and I'm not getting the same thing. I ...
0
votes
2answers
114 views
Pointers and asterisks
I searched and found Luke's very detailed reply to a similar question, however, my question (and confusion) still remain.
I don't understand why we can malloc a pointer to a struct, and this also ...
0
votes
1answer
39 views
PSET5: memory leak in check function
bool check(const char *word)
{
unsigned int hash_index = hash(word);
node *trav = table[hash_index];
while (trav != NULL)
{
int len = strlen(trav->word);
char ...
0
votes
1answer
124 views
Speller Valgrind leaks bytes + error: munmap_chunk(): invalid pointer error in C
Check50 gives me the munmap_chunk: invalid pointer - it seems I am not copying something right with strcpy.
Valgrind gives me: LEAK SUMMARY: still reachable: 608 bytes in 2 blocks
==2864== 56 bytes ...
0
votes
1answer
31 views
pset4 speller trie segmentation fault
I am doing the trie version of speller in pset4 and keep getting a segmentation fault.
I have run my code on short dictionaries and short text files and it seems to work just fine but when I try ...
0
votes
1answer
105 views
PSET4 (Speller) malloc and calloc usage
After getting my code to work, i looked if there were any memory leaks using valgrind. It found no memory leaks, however it returned these two errors:
==7109== Conditional jump or move depends on ...
0
votes
1answer
91 views
PSET4 free on malloc in hash function
I'm trying to improve my hash function in Speller and I'm having trouble freeing allocated memmory.
I'm getting * Error in `./speller': free(): invalid pointer: 0x0000000001a02252 *
Aborted
I know ...
0
votes
1answer
95 views
Pset5 why calloc works and malloc doesn't ?
I wish i could understand better the application of malloc and calloc, i was using malloc to allocate memory for the root in my code and had the following error on valgrind:
==20066== Conditional ...
0
votes
1answer
193 views
PSET4: free(): invalid next size (fast)
So as the title says, I'm trying to do the pset4 where I get this error when I try to execute the program. I've searched the forum and also Reddit, and I understood that I've some issue with the ...
0
votes
1answer
34 views
Errors from context when running trie dictionary from pset5 speller through valgrind
I've managed to implement a trie data structure for speller, and it seems like there are no memory leaks, but when I run valgrind -v ./speller texts/lalaland.txt I get quite a lot of errors from ...
0
votes
1answer
83 views
PSet5 Hash Tables
I was learning how to create an array of linked lists for the pset5 problem. But i keep getting a segmentation fault when I go through a character linked lists a second time. Some kind of address keep ...
0
votes
1answer
10 views
for cicle itrations
hi guys im wrote testing program to test features for my function and there is only 7 iterations in my for cicle but i malocc`ed more then that tell me why pls(testing string was andrew8mike)
#...
0
votes
1answer
31 views
What will happen if you assign a static value to a pointer in C?
In this example, what will it happen if I assign for example:
pk = 6;
Thanks!
0
votes
1answer
615 views
pset4 recover.c - working with fread() and malloc()
I'm attempting recover.c and I'm interested in clearing up a few things about fread() and malloc().
I tried to sample the first few bytes of the card.raw file but I keep getting the same two errors: ...
0
votes
1answer
605 views
Assigning an empty array with malloc has a random number in it
Im trying to debug why my helpers.c in the find pset is not working perfectly. I kept getting random large numbers in my array and I kept going up the ladder in the function to the point of ...
0
votes
1answer
225 views
pset 4 recover - segmentation fault with malloc
I seem to be stuck on pset4 recover and would appreciate some help! I think I understand the idea of the problem set by now but I've done approached the problem a bit unconventionally and keep getting ...
0
votes
1answer
33 views
PSET 6 Problem with malloc() on parse function
I can't figure out this problem, I hope someone can help me.
My server works perfectly only for the first HTTP request, but when I try to request something else, it throws me an error. This is a copy ...
0
votes
1answer
354 views
pset6 parse function: Invalid read of size 1
I'm having trouble with allocating memory correctly.
p is a pointer that I intended to point to method, target, then http switching to the next one after each space is found.
Then I thought I'd be ...
0
votes
1answer
49 views
check50 fails on caesar.c when using free()
I have a little problem. I can get get this to pass all the checks, but only if I remove the free() statement on L71
Link to code removed by andy5995
If I leave the free() statement in, this is ...
0
votes
1answer
571 views
pset4 resize: how to copy a row
Just spent 2 days for figuring out how fread(), fwrite() and fseek() works.
I tried to use "Rewrite" method from Zamyla's video for vertycal resizing:
- Remember pixels in array (first written row of ...
0
votes
1answer
140 views
Kinda confused with what needs memory allocated in pset5
I wanted to give hashtables a go with pset5. I've set the struct up as:
typedef struct node {
char *data;
struct node *next;
} node;
Every time I link a new node all of the node->data ...
0
votes
1answer
198 views
pset 4 Recover creates 50 corrupted or mainly grey images
I wanted to try using malloc and a BUFFER structure of 512BYTES for this exercise with the intention of creating a file if the 4 signatures of a JPG are detected and fwriting the struct of 512B into ...
0
votes
1answer
464 views
pset4 malloc() approach. Help with size of buffer
I'm having some trouble with the malloc function.
I want to make a buffer the size of the new row I'm going to write in the resized file, and this is my approach.
I must say that bi.biWidth is ...
0
votes
1answer
26 views
PSET6 - Why is my filename string getting weird characters after two refreshes?
This is my code to extract the filename requested from the server from the request message:
char* buffer2 = strchr(buffer1, '/');
char* buffer3 = strchr(buffer2, ' ');
char* buffer4 = malloc(strlen(...
0
votes
1answer
74 views
How can I avoid a Segmentation fault in my Recover.c
I have looked thoroughly through other solutions, but they tend to be specific to another person's code. I have also used Valgrind to try and isolate the problem, and considered that I may have to use ...
0
votes
1answer
408 views
Bad pointer null assignment followed by malloc fail — WHY?
I'm stumped! In dictionary.c I have coded the load function (with more code that follows the bug, but not needed for this question.) One small block of code is producing a problem! Assigning NULL to ...
0
votes
1answer
93 views
Garbage values when creating new node
So, for my load function in pset6, I'm creating a new node for the current char if it isn't found in the children.
node* node_cur = &root_node;
loop iterate over chars in word
{
if(node_cur-...
0
votes
1answer
74 views
PSET 4: Resize. Does not work with dynamic buffer, only static
I managed to make resize work using a static array to store a row of pixels for the outfile (rewrite method). However, my first attempt with a dynamic array doesn't work, and I don't understand why. ...
0
votes
1answer
208 views
Why we use sizeof(char)
Can anyone please explain?
char *s = get_string("s: ");
if (!s)
{
return 1;
}
// allocate memory for another string
char *t = malloc((strlen(s) +1) * sizeof(char));
if (!t)
{
return 1;...
0
votes
1answer
75 views
pset5 speller unload - node allocation quirk
Most of this pset5 has gone smoothly, but unload() has caused me problems. When I'm navigating down my data structure (trie) to locate a node with all NULL children, the last index has a memory ...
0
votes
1answer
41 views
Last word of dictionary file replaces all the nodes in node bucket
Currently I am working on the load function using a hash table with singly-linked list. I have tested the create(), insert(), and find() function in a separate file and they work as expected.
...
0
votes
1answer
71 views
PSET5. Free a variable outside a loop. leaking memory
I've been stuck for days in the implementation of LOAD with a TRIE data structure.
I think my code works (well it doesn't show seg faults) but I am getting a lot of memory leaks.
I implemented the ...
0
votes
1answer
64 views
pset5 can't figure out what's wrong! segmentation fault
I have no idea what I am doing wrong in this pset! I feel very lost. Anybody have any pointers on where to even begin with what I'm doing wrong? Some specifics -- I am getting a segmentation fault ...
0
votes
0answers
45 views
I am trying to use this code segment to know the execution time of the C program by initializing the matrices a,b and c.Can someone help?
This is the question
/* code segment */
for (k=0; k<n; k++)
{
for (i=0; i<n; i++)
{
r = a[i][k];
for (j=0; j<n; j++)
{
c[i][j] += r + b[k][j];
}/* end for…...
0
votes
1answer
1k views
malloc and fgets
#include<stdio.h>
#include<cs50.h>
int main(void)
{
char* s= malloc(sizeof(char)*5)); //allocating 5 bytes
fgets(s,6,stdin); //allocating 5 bytes for hello and 1 byte for '\0'...
