Questions tagged [pointers]
The pointers tag has no usage guidance.
141
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How can I fix this double free in speller?
I've posted this question previously but I tried to post various functions from my code without posting the whole code at once, because I thought that was better etiquette or something. However, the ...
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0
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34
views
Speller: Valgrind tests fail; problem may be with load
My spell checker seems to run pretty well, except the unload function never ran properly. It compiles, but executing it prints out the misspellings but then prints the message, "double free ...
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0
answers
17
views
Inheritance, Lab 5: question on pointers
I am confused about the use of pointers in the array 'parents'.
typedef struct person
{
struct person *parents[2];
char alleles[2];
}
person;
Isn't an array itself a pointer? to its first ...
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0
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157
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"Format specifies type 'int' but the argument has type 'int * "-- at C
I have a problem with the main program , the main get an array - dynamic and didn't print the actual result I need.
int main()
{
int arr[] = {1,2,2,4,1};
int n = 5;
int* ptr = NULL;
int iseven = 1;
...
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0
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12
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where is the memory leak in my code?
cant find where is the memory leak
here is my code
// Implements a dictionary's functionality
#include <stdio.h>
#include <ctype.h>
#include <stdbool.h>
#include <string.h>
#...
1
vote
2
answers
62
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Week 4 lecture: can't reproduce string != string
In the lecture of week 4 in CS50x, David illustrates how two strings can't be compared with two equal signs (==), and instead, strcmp() has to be used.
I can't reproduce this locally or on CS50's IDE ...
0
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1
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208
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pset5 - speller "double free detected" when I run check 50 but program does nothing during self tests
I am currently doing Speller. I have written all the functions and the program compiles but during self testing it is printing "misspelled words" and stays stuck at a blinking cursor. It ...
- 17
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1
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174
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(PSET 4 - Recover) Why is first recovered image blank?
I am on problem set 4 recover and I have nearly completed it. I have written my code and it compiles but when I run it on the card.raw file it appears to recover all the 50 photos except the 1st one ...
- 17
1
vote
1
answer
28
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Pointers Memory Allocation
Here I have a user-defined structure "person" that stores two pointers one for the name and one for the phone number.
I create an array people of length 2 of type person.
Each of the ...
- 32
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1
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28
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Week 4 Memory - Swap
Does the = (assignment) get me a copy of the content or points me to the same location in memory?
For some reason, I end up thinking that what the code does is not setting y = 44 in a separate memory ...
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1
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2
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46
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Blur PSet4 (Filter) - Compilation errors passing reference to the image[height][width] array in helper function using pointers
I'm having a brainfart wrapping my head around the use of pointers when trying to pass a reference to the image 2D array in a helper function that I created to assist in the blur effect.
Here's blur:
...
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1
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120
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PSET4 Blur not passing Check50
My code seems to work (when visually inspecting output files), but Check50 does not pass it. I'm struggling to understand what is causing this issue despite having repeatedly read over the code and ...
0
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1
answer
473
views
incompatible pointer types error
I'm working on lab5, inheritance, and I'm trying to decipher why I'm getting this error when trying to compile:
inheritance.c:52:32: error: incompatible pointer types assigning to 'struct person *'
...
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1
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27
views
Why is the reference variable for dynamically allocated memory lower on the stack?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
int n = 5;
char str1[n];
char *str2;
char str3[] = "World!";
// ...
0
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1
answer
200
views
PSET2 Caesar - Stuck at 'isdigit' step: Do I need to learn about pointers, or is something else going on?
Here is what I am attempting, and my errors. I am gathering that I am not grasping the "array of strings nature of argv[], and since I am following along with the material from class, I am pretty ...
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1
answer
23
views
pointers and addresses
int m=10;
int *ab=&m;
printf("address of *ab:%p\n",&*ab);
printf("adress of ab:%p\n",&ab);
output:
address of *ab:0x7ffd85fddefc
adress of ab:0x7ffd85fddf00
i ...
0
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1
answer
157
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PSET4 filters helpers.c
I need some help with pointers, mostly. I've malloc'd a BUFFER pointer to the struct data type RGBTRIPLE. Though I can't access its properties.
// Reflect image horizontally
void reflect(int height, ...
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0
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1
answer
49
views
CS50 Pset4 Logic Problem
I am 3 days into PSET 4 Recover.
In PSET 4 we are supposed to create a program which inputs a memory card and scans through that memory card for the signatures of lost JPEG files. Once the header of a ...
0
votes
1
answer
50
views
I know that my recover is wrong, but I'm not sure what steps to take-
I 'm getting a segmentation fault for my recover code. I know that it's wrong, and I think that this boils down to me not really understanding how to apply pointers/file functions. Maybe you could ...
- 17
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1
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43
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pset4 recover - how can I get last few bytes to JPG
I've finally gotten recover.c to the point where it compiles. When I run it, it gives me this error message:
munmap_chunk(): invalid pointer
Aborted
But it also generates all fifty of the pictures! ...
- 19
0
votes
1
answer
1k
views
Pointer passed as argument, then suddenly goes null
In the main method I declare a character pointer pCharacter. I pass this variable to the setCharacter method and assign it an address and a variable gets assigned to that address.
From what I ...
- 3
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1
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268
views
Confusion about comparing strings and int/char
This question concerns variables, pointers and addresses as addressed in Lecture 4. I understand that strings are not "real" in the way that integers and characters are, and are just defined as "...
- 165
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1
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17
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writting a function to display a file
in the week 4 shorts, it was told how we can write cat command from linux in c:
i Wrote the following code:
#include <stdio.h>
include
void Print_File(FILE *f)
{
char s = fgetc(f);
while (s ...
- 51
0
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1
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586
views
What does a pointer to a file really represent?
I have a question regarding file pointers (i.e FILE *).
I am having a hard time understanding conceptually what this represents in terms of its memory.
When the concept of files was introduced in ...
0
votes
1
answer
166
views
Replacement of string with char* in any general case
Take a simple program where i want to count the number of vowels in a string, this i've easily implemented using string.h. But when i try that with char*:
#include <stdio.h>
int main(void)
{
...
- 51
0
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1
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41
views
Pointer Initialization and Free, Help!
If you initialize a pointer (trav) and assign it another pointer, should you and what happens if you free trav? thank you!
node *table[N] = { NULL };
trav = table[i];
Also, should malloc be called ...
0
votes
1
answer
554
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 ...
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0
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1k
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"Still reachable" in Valgrind
I have noticed on a few programs that, while none of them have any memory leaks, flag a "still reachable" message when run via valgrind.
Does "still reachable" simply mean that there are pointers in ...
- 15
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1
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28
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Understanding pointer variables
I'm trying to understand pointer variables. I have the following sample program:
#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <...
- 3
0
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1
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14
views
How do I change the value of "a" via "b"?
e.g.
Input:
int a = 1;
int b = a;
b = 5;
printf("%i \n", a);
Output:
5
I have tried writing things like
int* b = &a;
b = 5;
However i cant change b into an integer from a pointer?
0
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1
answer
133
views
the difference between string pointers and int pointers
why does the compiler act in a different way when a string is initialized or declared than it does in case of an integer pointer ?
i mean we do that
char *x = "cat"
not
char* x = &(of ...
0
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1
answer
2k
views
Pointer error - member access within null pointer of type 'node' (aka 'struct node')
I am trying to create a function that will malloc my node pointers but for whatever reason the passed node when accessed after my function throws an error as if the node was not given memory at all. ...
- 1
0
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1
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897
views
Pset2 Vigenere: Pointers/Function Question
I've been having major trouble with Vigenere. I've worked on it every day for the passed two weeks and each day, I solve one problem but encounter another. I was able to get the program with the ...
1
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1
answer
309
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vigenere output "incompatible pointer types"
I'm trying to solve pset2 vigenere, but I'm having some troubles. I'm using two functions to adapt the key to the text and then to apply the cipher. When I run the last function, I can't get any ...
- 25
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2
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556
views
How to convert char to integer? PSET4
int main(int argc, char *argv[])
//Remembers n
int n = *argv[1];
I'm trying to access the value n as an integer. However, when I do this, n stores the ASCII code for the number (I think!). I have ...
- 13
1
vote
2
answers
1k
views
Printf doesn't print whole string "11111"
String a, that is a pointer, contains 5 1's, but printf outputs only one 1.
#define _XOPEN_SOURCE
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#...
0
votes
1
answer
80
views
pset5 (trie) valgrind memory leak
I'm having trouble with the last step of pset5, valgrind. When I run it with the test text I get: Looks like you're trying to access 8 bytes of memory that isn't yours? Did you try to index into an ...
- 21
1
vote
1
answer
97
views
Pointers to strings
I have yet another question regarding pointers to strings. I want to know why this code works fine, and by that I mean that it can change the char d to the char Q.
char Name [] = "Andrew B. Mayfair";
...
0
votes
2
answers
122
views
Segmentation fault in recover pset4
I am working on recover in problem set 4. However, after trying out different stuff, the code itself compiles but I get a segmentation fault and the outcome is only one jpg file called 000.jpg. I am ...
- 3
1
vote
1
answer
15k
views
pset1 Error: indirection requires pointer operand
Here is a snippet of my code:
long long card = get_long_long();
long long *FindLength = *card;
long long *FindFirstTwoDigits = *card;
And here are the errors:
credit1.c:8:29: error: indirection ...
- 15
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1
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2k
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Incompatible pointer types even though they are both char*?
dictionary.c:70:20: error: incompatible pointer types passing 'char *[46]'
to parameter of type 'const char *' [-Werror,-Wincompatible-pointer-types]
if (strcmp(checker->word, lowword) == 0)
...
2
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1
answer
26
views
Using * and & both works
SPOILER ALERT THIS CODE ALREADY WORKS SO DON'T LOOK IF YOU'RE STILL SOLVING
I'm just wondering why my code still works even if I change fwrite(buffer, 512,1, img); to fwrite(&buffer, 512,1, img);
...
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1
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14
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How can I ensure I'm changing the reference, not a copy, in this C function?
I'm trying to assign a pointer to a pointer within a function. I've passed pointers in and I'm trying to make the change inside. It is not happening, however. The issue is regarding the insert ...
0
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1
answer
26
views
Why am I able to insert an element into a hash tree via Main() but not via a function call?
I'm fairly certain this has something to do with pointers and the function using copies instead, but I'm not sure how...because I've inserted the pointer as a parameter for create();
#include <...
0
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1
answer
140
views
pset5 load null pointer issue
Working through the load portion of pset5. Everything compiles, but when I run valgrind it looks as if nothing is actually loading in, with the error of "null pointer passed as argument 1, which is ...
- 37
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1
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213
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recover pset4 file handling
I got this code to work, but I have a few questions for my own clarification.
On line 68 where I define the jpg title, why is it a single character? The actual title 001.jpg is much longer than a ...
- 17
2
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2
answers
13k
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pointers and scanf : when do I use &x, *x or just x?
The following code works but why do I have to use 'x' instead of '&x' inside scanf()?
```
#include <stdio.h>
#include <stdlib.h>
int main(void) {
char *x = malloc(sizeof(char) *...
- 59
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1
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60
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pset1 credit various errors: incompatible pointers, undeclared identifiers
I tried to compile this:
#include<stdio.h>
#include<cs50.h>
char get_credit_card_status(long long credit_card_number, char Luhn_check)//, char credit_card_status)
{
char ...
- 1
0
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1
answer
46
views
sizeof() syntax error with node pointer
Is there something wrong with my syntax? Won't compile, apparently because of line:
sizeof(node->sprouts) / sizeof(node)
above node defined as follows:
typedef struct node
{
bool is_word;
struct ...
- 11
0
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1
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127
views
What is correct syntax when declaring a pointer? (i.e. where to place the *?)
I'm a bit confused as to where to place the * when declaring a new pointer.
For example, let's say I've made a linked list and declared a custom structure node.
I've noticed when I was making ...
- 119