Questions tagged [pointers]

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The load function in speller is returning a seg fault

I've run the debugger on my faulty program and reached the conclusion that the main that's causing the problem is among the following: while(fscanf(f, "%s", term) != EOF) { ...
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28 views

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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29 views

(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 ...
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15 views

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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9 views

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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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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1answer
53 views

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 ...
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74 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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20 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!"; // ...
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According to CS50 Lecture 4 on Memories, my code should not be able to compare two strings and print"same". But it does print "same". Why?

Was expecting it print out "different" since I've created 2 different variables and stored the same values MANUALLY TYPED OUT. According to lecture 4, strings are pointers and when compared, ...
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56 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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11 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 ...
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44 views

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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46 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 ...
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45 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 ...
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39 views

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! ...
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309 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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1answer
58 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 "...
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1answer
13 views

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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207 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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47 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) { ...
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32 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 ...
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380 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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983 views

"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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21 views

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 <...
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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?
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48 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 ...
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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. ...
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896 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 ...
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206 views

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 ...
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446 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 ...
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2answers
892 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> #...
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75 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 ...
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1answer
33 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"; ...
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120 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 ...
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1answer
9k 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 ...
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1k views

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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1answer
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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11 views

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 ...
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23 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 <...
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120 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 ...
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1answer
200 views

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 ...
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2answers
8k views

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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58 views

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 ...
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1answer
36 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 ...
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1answer
86 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 ...
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74 views

SPELLER-Create Global struct definition and global struct instance

I am working on SPELLER and am stuck on the load function. I have no errors the way it's written but the problem is in this code's location. typedef struct node { ...
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105 views

Two hash table questions

I am working through SPELLER and have a few questions. When I create a new node node *newptr = malloc(sizeof(node)); do I need to say newptr1, newptr2, newptr3 and if so what is the best way of doing ...
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84 views

pset4 whodunit can't understand the infile pointer

In this whodunit copy.c the input filenames and output filenames are entered as command line arguments but I couldn't understand that How does inputting the file name will point to the file. // ...
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123 views

Pointers: What is the difference between char * <name> = .... and char* <name> = .... in assignment operations

In problem set 5, there are these two lines of code. char* dictionary = (argc == 3) ? argv[1] : DICTIONARY; ... char *text = (argc == 3) ? argv[2] : argv[1]; Both of theses operations seem to define ...