Questions tagged [pointers]

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*--ptr = ""; warning

I am copying one array into another using pointers, and one value in the array I have to fill in "by hand" if a certain condition happens. Please, help me to understand what shall I do to assign ...
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Having some issues understanding how pointers work and how to pass them to functions and use them

int* create_random_array(int n){ int arr[n]; srand(0); for (int i = 0; i < n; i++) { // Fill with random ints 1-100 arr[i] = (rand() % 100)+1; } return arr;...
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Help needed for pointers in C

I need a bit of help for my following program which inputs a string from the user and also prompts from the user a character from that string so as to display the number of times that character is ...
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1 answer
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Issue with the cs50 c compiler

Unable to use pointer as used normally. While executing ** int a = 3; printf("%d", &a); ** This should print address of variable a. But it gives an format specifier error.
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1 answer
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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 <...
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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
1 answer
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References and Pointers

What is the difference between a reference variable ( eg int& ref) and a pointer variable ( int*pointer ).
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1 answer
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Problem with pointers, getting seg fault while indexing with variable instead of plain number

I would like to ask why is that giving me seg fault. int **a = (int**) malloc (sizeof(int*) * 3); a[0][0] = 1; a[0][1] = 2; a[0][2] = 3; for(int i = 0; i < 3; i++) { printf("%d",...
1 vote
1 answer
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pset 4 - recover -> invalid pointer

i am trying to solve the recover issue. When I run my programm I get: * Error in `./recover': free(): invalid pointer: 0x0000000001da5200 * Aborted I don't know how to proceed. Can someone please ...
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1 answer
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More pointer concepts

I think that I have the basic concept of pointers pretty clear now (after considering it, reading and re-watching the course material a few times) but I still have a question. A pointer is ...
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1 answer
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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. ...
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1 answer
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I've use array pointer method in pset2 (initials.c) but it return "Segmentation Fault (Core Dump) Why?

I'm working on pset2 using array pointer method, but unfortunately, the program return "Segmentation Fault (Core Dump)" I've post a picture of my code below.Can I use this method? or I have to use if ...
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pset4, blur, filter-less ...using POINTERS and NULL character

I've been working on blur from PSET4, filter-less for about a week now. I've been trying to filter those pixels with no content by copying the image pixels into a pointers array. Then, I paste NULL ...
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1 answer
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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) ...
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1 answer
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pset4 increment pointer of type RGBTRIPLE by BYTE

In pset4, resizing an image, I decided to try out pointers and memory allocation to learn more about it, but I've run into an issue with my approach... I've created a pointer and allocated memory for ...
1 vote
1 answer
333 views

PSET5 - Issues with initialization of pointers in LOAD function

I'm still trying to debug my load function, I rewrite my code again and again but with no result... I know we need to have specific question, but now I just have so many questions. So, I'll go with ...
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1 answer
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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!"; // ...
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Why the pointer value changed in here?

from my understanding for pointers in c, when we use a pointer for string, it refers to the address of the [0] element of that string, which means this 4 lines of code should be the same result: char *...
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2 answers
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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 answer
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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 ...
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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 ...
1 vote
2 answers
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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 ...
2 votes
2 answers
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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) *...
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1 answer
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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 ...
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1 answer
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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 ...
1 vote
1 answer
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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 ...
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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 <...
23 votes
2 answers
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Difference between char and char* in c

suppose we declare two variable char s[]= "hello" char* p = "hello". what is the difference between these two?
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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 answer
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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 votes
1 answer
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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 *' ...
1 vote
1 answer
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C: Vigenere - incompatible pointer types passing 'char **' to parameter of type 'const char *

I'm trying to iterate repeatedly over key (a word) which the user inputs on the command line. This keyword is used to encipher a word which the user inputs when prompted by the word 'plaintext'. I ...
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1 answer
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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
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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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1 answer
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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
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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 ...
0 votes
1 answer
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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! ...
0 votes
1 answer
686 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 ...
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2 answers
121 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 ...
0 votes
1 answer
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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 "...
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1 answer
336 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 ...
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1 answer
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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) { ...
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1 answer
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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 ...
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1 answer
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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 ...
2 votes
1 answer
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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 ...
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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 ...
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1 answer
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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?
2 votes
2 answers
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Pointer Concepts

I am problem set 6 and very confused by the use of pointers. Please tell me the difference of these things first? What is the difference between char word[length] and char *word = malloc(sizeof(char) ...
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1 answer
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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 ...
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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 ...