Make own strrchr() function but case-insensitiv

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• How do I manipulate the contents of a stat() struct?

  I have a stat struct, and I'm looking for a way to get data out of it to be manipulated. The program will successfully run and print the desired st_mtime value, but including either of the "seg-fault" lines below causes a segmentation fault in runtime.

          struct stat buf;
          time_t time_m;
          time_t sys_time = time(0);
          if(stat(sub_dirp->d_name,&buf)==0)
                   {
                       //time_m = buf.st_mtime;                                     //seg-fault
                       //double since_last = (difftime(sys_time, buf.st_mtime)/60); //seg-fault
                       printf("%d ", (int)buf.st_mtime);                          //This works.
                   }
  

  Both lines are attempting to manipulate the buf.st_mtime value in some way.

  I've had a hard time finding any examples of the usage of stat() that do anything other than print its contents, which makes me wonder if it's even possible.

  So my question is, if it is possible, what am I missing?

  P.S. I do wish to keep st_mtime in the Unix timestamp format to make it easier to manipulate.

  Edit: After realizing that st_mtime is itself its own struct (timespec), how can I access the st_mtime.tv_sec member?

  The compiler doesn't like buf.st_mtime.tv_sec one bit.

  compiler error
• What's purpose of __linecapp in getline, when it'll auto resize?

  It's all about second parameter of getline in stdio.h,

  I'll name it 'n' or '__linecapp' below.

  According to the document:

  If the buffer is not large enough to hold the line, getline() resizes it with realloc(3), updating *lineptr and *n as necessary.

  It'll automatically update line capacity, then why should we input __linecapp?

  P.S Someone ask before, but discussion didn't explain when we need it, or how to make it useful.
• Linked List Deletion function causing program to crash *wrong pointers?*

  In my program when a username is following another one and also has posted a "tweet" which is a string in an attempt to delete the followed username it breaks the program. I believe this is the code snippet in question. If anyone could help me identify the issue I would be thankful as I am learning the usage of linked lists for scale able projects. Thanks

  void deleteAccount(accountNodePtr *startPtr, accountNodePtr *curAcPtr, tweetsNodePtr *startTwtPtr){
  accountNodePtr acLoopPtr;
  accountNodePtr tempCur = *curAcPtr;
  followNodePtr followingPtr = tempCur->followingPtr;
  followNodePtr tempPtr;
  followNodePtr tempPtr2;
  tweetsNodePtr iterTwtPtr;
  iterTwtPtr = *startTwtPtr;
  *below here in question*
      tempCur = *curAcPtr;
  while (tempCur->followersPtr!=NULL){
      acLoopPtr = *startPtr;
      while (strcmp(acLoopPtr->username, tempCur->followersPtr->username)!=0){
          acLoopPtr=acLoopPtr->nextPtr;
      }
  
      if (strcmp(acLoopPtr->followingPtr->username, tempCur->username)==0){
          tempPtr=acLoopPtr->followingPtr->nextPtr;
          free(acLoopPtr->followingPtr);
          acLoopPtr->followingPtr=tempPtr;
      }else{
          tempPtr=acLoopPtr->followingPtr;
          while(strcmp(tempPtr->nextPtr->username, tempCur->username)!=0){
              tempPtr=tempPtr->nextPtr;
          }
          tempPtr2=tempPtr->nextPtr->nextPtr;
          free(tempPtr->nextPtr);
          tempPtr->nextPtr=tempPtr2;
      }
  
      tempPtr = tempCur->followersPtr->nextPtr;
      free(tempCur->followersPtr);
      tempCur->followersPtr=tempPtr;
  }
  

  This is the structure

  typedef struct followsNode {
  char username[MAX_USERNAME];
  struct followsNode *nextPtr;
  } followNode;
  
  typedef struct accountsNode {
      char username[MAX_USERNAME];
      struct followsNode *followersPtr;
      struct followsNode *followingPtr;
      struct accountsNode *nextPtr;
  } accountNode;
  
  typedef followNode *followNodePtr;
  typedef accountNode *accountNodePtr;
  
• After using .NET upgrade assistant on C# solution, why does .StartsWith give a false positive?

  I updated my solution from .NET 4.8 to 6.0 and it builds and runs fine after fixing references, but now using StartsWith with chars gives an unexpected result.

  A string that starts with the chars \0\0\0 evaluates as True when using:

      example.StartsWith(new string(new char[] {'\u0003', '\u0005', '\0'}));
  

  From what I've seen maybe this has to do with culture? Do I need to make a new StartsWith function that compares each character one at a time? example[0] == '\u0003' is still obviously False.
• How do you check if the user input is a single Char

  I'm trying to write a program where if the user enters a single character, the program displays True on screen, otherwise if multiple characters are entered it prints False.

  public class FinalExamTakeHome8 {
      public static void main(String[] args) {
          try (Scanner kbd = new Scanner(System.in)) {
              System.out.println("Enter an item");
              if (kbd.hasNextInt() || kbd.hasNextChar() || kbd.hasNextDouble()) {
                  System.out.println("True");
              } else {
                  System.out.println("False");
              }
          }
      }
  }
  
• No suitable function from string to char exists

  I'm fairly new to C++ and have been messing around with classes lately. In my problem I need to take in the ticket name and number and make functions that tell the user if the seat is available or not. If it is not available, the seat can be booked and needs to be stored. To solve this problem, I created a dynamic array that takes in the seat information and grows by length everytime a seat has been booked. Since this array takes in strings, I also defined it as a string. However, when I try to store in the seats and row names, I get an error that says that a string cannot be converted to a char. I tried to change the array to char type but that did not do the trick. Below I have added my code (sorry it's some what lengthy) with explanation. Hopefully I have provided you with enough info, thanks a lot!

  #include <iostream>
  #include <string>
  #include <cstring>
  using namespace std;
  
  //Initializing Ticket class
  
  class ShowTicket{
      public: //Defining variables
          string row;
          string seatNumber;
          bool sold; //true or false statement if the seat is available or not
          string status;
          int size;
          string *arr = new string[size,2];
  
          int *newSize = &size; //pointer that points to size and changes +1 length if 
                                //seat gets booked
  
      //Constructor
      ShowTicket(string rows, string seatNumbers){
          row = rows;
          seatNumber = seatNumbers;
          sold = false; //Seat is available by default untill it gets booked
          status = "available"; //printing that the seat is available by default, untill 
                                //it gets booked
          string *arr = new string[size,2]; //2D dynamic array that grows in size and 
                                            //stores seat number and row
      }
  
      bool isSold(string row, string seat); //function taking in row and seat and checks 
                                            //if the seat is available
      void sell_seat(string row, string seat); //function that sells a seat and stores it 
                                               //in arr
      string print_ticket(string row, string seat);//function to print the ticket info
  
  
  };
  
  bool ShowTicket::isSold(string rows, string seats){
      for(int i; i<= size; i++){ //for loop to loop over each element of the array
          if (arr[i][0] != rows && arr[i][1] != seats){//check if each element matches 
                                                       //with a sold ticket, if not it 
                                                       //returns sold = false
              return sold; 
          }
      }
  }
  void ShowTicket::sell_seat(string row, string seat){ //This function adds 1 element to 
                                                       //to pointer array to store in new 
                                                       //data
  
      *newSize = size+ 1; //new size is initialized and with that size is incremented by 
                          //+1
      string *temp = new string[newSize,2]; //temporary array is created with the new size
      for(int i; i <size; i++){
          temp[i] = arr[i]; //temporary array copies data from array
      }
      delete [] arr; // old pointer array is deleted to avoid memory leaks
      arr = temp; //array is pointing to array with +1 length 
  
      arr[*newSize][0] = row; //new ticket info is stored in the newly created space
      arr[*newSize][1] = seat; //^^
  
      sold = true; //giving info that the ticket is indeed sold
      status = "sold"; //when calling the function, it now also prints the ticket is 
                       //stored
  }   
  string ShowTicket::print_ticket(string row, string seat){
      string a = "";
      cout << row << " " << seatNumber << " " << status; //printing ticket info
      return a;
  }
  int main(){
      ShowTicket myticket1("AA","101"); //creating tickets with input
      ShowTicket myticket2("AA","102");
      ShowTicket myticket3("BB","103");
  
      if(!myticket1.isSold()){//checking if the ticket is already sold
        myticket1.sell_seat();//if not, it is bought
  
      }
      cout << myticket1.print_ticket() << endl; //printing ticket information
      cout << myticket2.print_ticket() << endl;
      cout << myticket3.print_ticket() << endl;
      return 0;
  
  }
  
• Difference between " %[^\n]%*c" and " %[^\n]" for consecutive scanf in C

  I've been trying to scanf multiple consecutive strings.

  I know you have to eliminate the newline character and i've also been told that "%[^\n]%*c" is the RIGHT way. But in my tests, " %[^\n]" works even better because it's simpler and also doesn't go wrong if i try to feed it a newline directly, it keeps waiting a string. So far so good.

  Is there any case in which "%[^\n]%*c" is the better way?

  Thanks a lot!
• Make own strchr() function but case-insensitive

  My exercise requires that I can use case-insensitive input. My approch is that I use the tolower and toupper function.

  How can I convert the array to lowercase letters?

  void KULstrcichr(char *arr, char search)
  {
      printf("Return value when uppercase character %c is passed to isupper(): %d\n", search, isupper(search));
      // The  strchr() function returns a pointer to the first occurrence of the character c in the string s.
      if (isupper(search))
      {
          printf("Groß\n");
          char lowercasesearch = tolower(search);
          printf("Das ist der Output: %s", arr);
          char *ptr = strchr(arr, lowercasesearch);
          printf("Das ist der Buchstabe: %s", ptr);
      }
      else
      {
          printf("Klein\n");
          char upercasesearch = toupper(search);
          printf("Das ist der Output: %s", arr);
          char *ptr = strchr(arr, upercasesearch);
          printf("Das ist der Buchstabe: %s", ptr);
      }
  }
  
• find elements of an array in another array, why do I have this error?

  I was trying to visualize the algorithm of this exercise, but I'm having a lot of problems.

  the exercise asks to implement this function:

  extern const void *memmem(const void *haystack, size_t hsize, const void *needle, size_t nsize); 
  

  • haystack and needle are two pointers to two different areas of memory. haystack points to a memory of size hsize, and needle points to a memory of size nsize.
  • find *needle elements in *haystack, and if *needle elements are in *haystack too, return a pointer to the new allocated memory (containing *needle elements) and this pointer has to point to the 0-th element of the new memory.

  I hope I've explained it better than the original exercise (it's not clear, so I had a hard time trying to understand it).

  ---

  I've tried to sketch the algorithm this way:

  algorithm accepts two pointers and their sizes. (loop) increment *needle by one at each step in order to find a common element (comparing that element with the current element of haystack), and if that condition is true, increment a counter by one. Doing this way I've obtained the length of the final array. Then, I allocate enough memory, and do another loop to copy each element in the final vector. last but not least, return this pointer.

  this is how is it suppose to look like in code (I know it's not complete, but I'm currently building it step by step, it's not easy at all):

  #include <stdlib.h>
  const void* memmem(const void* haystack, size_t hsize, const void* needle, size_t nsize) {
      if ((hsize == 0) || (nsize = 0)) {
          return NULL; // here, I should've done a NULL pointer exception check too, because haystack and needle may be null pointer too. for now, ignore that. 
      }
      for (size_t i = 0; i < nsize; i++) {
          if (needle[i] == haystack[i])
      } 
  
  }
  
  
  int main(void) {
  
      int haystack[] = {-1, 0, 1, 2, 3, 4};
      size_t hsize = 6; 
      int needle[] = {-1, 8, 4, 2};
      size_t nsize = 4; 
  
      int* ptr = memmem(haystack, hsize, needle, nsize); 
  
  
      return 0; 
  }
  

  the crucial part is here:

  for (size_t i = 0; i < nsize; i++) {
              if (needle[i] == haystack[i])
          } 
  

  because I have this error: expression must be a pointer to a complete object type. What does it mean? I've never heard of this error message before. arrays are complete, I've defined them correctly, therefore I don't know why I have that.
• Is it right to implement queue with single linked list?

  My Code ↓

  Some macros defined by

  #include <stdio.h>
  #include <malloc.h>
  
  #define  ElementType int
  
  #define  ERROR 0
  
  
  // 队列用单链表实现
  struct Node {
      ElementType Data;
      struct Node *Next;
  };
  
  struct QNode {
      struct Node *rear;
      struct Node *front;
  };
  typedef struct QNode *Queue;
  

  Add an element to the end of the queue

  void AddQ(Queue PtrQ, ElementType item) {
  
      struct Node *rearCell;
      rearCell = (struct Node *) malloc(sizeof(struct Node));
      rearCell->Data = item;
      rearCell->Next = NULL;
  
      if (PtrQ->front == PtrQ->rear && PtrQ->rear == NULL) {
          PtrQ->front = PtrQ->rear = rearCell;
      } else {
          PtrQ->rear->Next = rearCell;
          PtrQ->rear = rearCell;
      }
  
  }
  

  Delete the element from the beginning of the queue and return the element value.

  ElementType DeleteQ(Queue PtrQ) {
      struct Node *FrontCell;
      ElementType FrontElement;
      if (PtrQ->front == NULL) {
          printf("队列空");
          return ERROR;
      }
      FrontCell = PtrQ->front;
      if (PtrQ->front == PtrQ->rear)
          PtrQ->front = PtrQ->rear = NULL;
      else
          PtrQ->front = PtrQ->front->Next;
      FrontElement = FrontCell->Data;
      free(FrontCell);
      return FrontElement;
  }
  

  Initializing queues and calling

  int main() {
  
      Queue PtrQ = (Queue) malloc(sizeof(struct QNode));
      PtrQ->front = NULL;
      PtrQ->rear = NULL;
  
      AddQ(PtrQ, 999);
      AddQ(PtrQ, 88);
      AddQ(PtrQ, 77);
  
      ElementType value = DeleteQ(PtrQ);
  
      printf("%d\n", value);
  
      ElementType value1 = DeleteQ(PtrQ);
  
      printf("%d\n", value1);
  
      ElementType value2 = DeleteQ(PtrQ);
  
      printf("%d\n", value2);
  
      return 0;
  }
  

  It worked out as I expected.

  

  question if (ptrq-> front = = ptrq-> rear & & ptrq-> rear = = null)in AddQ. Is there a better judgment? and some other improvements

  I'm learning to implement queues in C.
• Why this function is not able to reverse the Linked List?

  I want to reverse a linked list but when i compile this code it terminates unexpectedly.

  #include <bits/stdc++.h>
  using namespace std;
  
  class node{
  public:
      int data;
      node* next;
  
      node(int val){
      data=val;
      next=NULL;
          }
  };
  

  For Inserting Elements in Linked List

  void insertattail(node* &head,int lol){
      node* n= new node(lol);
      if(head==NULL){
          head=n;
          return;
      }
      node* temp=head;
      while(temp->next!=NULL){
          temp=temp->next;
      }
      temp->next=n;
  }
  

  Display Function to print linked list

  void display(node* head){
      node* temp =head;
      do{
          cout<<temp->data<<"->";
          temp=temp->next;
      }
      while(temp!=NULL);
      cout<<"Null";
  
  }
  

  Function to reverse Linked List

  node* reverseit(node* head){
      node* prevptr= NULL;
      node* currptr= head;
      node* nextptr= currptr->next;
      while(currptr!=NULL){
          currptr->next =prevptr;
          prevptr=currptr;
          currptr=nextptr;
          nextptr=currptr->next;
      }
      return prevptr;
  }
  

  Main Function

  int main()
  {
      node* head= NULL;
      insertattail(head,1);
      insertattail(head,2);
      insertattail(head,3);
      insertattail(head,8);
      node* newhead= reverseit(head);
      display(newhead);
      return 0;
  }
  

  I think the problem is in logic of reverse function. I just used the code for linked list and made small changes.
• Is there a caseinsensitive version of strrchr and wcsrchr?(c++)

  I try to check if variable ends with expression.

  My current code is this:

  (strchr(variable.data(), tolower(expression[0])) || strchr(variable.data(), toupper(expression[0]))) && _stricmp((strrchr(variable.data(), tolower(expression[0]))? strrchr(variable.data(), tolower(expression[0])) : strrchr(variable.data(), toupper(expression[0]))), expression.data()) == 0

  It works. But with a case-insensitive version of strrchr and strchr I can simlpify it. I also need the case-insensitive versions of wcsrchr and wcsrchr for UTF16-strings:

  (wcschr(variable.data(), tolower(expression[0])) || wcschr(variable.data(), toupper(expression[0]))) && _wcsicmp((wcsrchr(variable.data(), tolower(expression[0])) ? wcsrchr(variable.data(), tolower(expression[0])) : wcsrchr(variable.data(), toupper(expression[0]))), expression.data()) == 0

  I´m open for other simplifications.

  I can´t write additional methods because the mainprogram is a vs-extension written in c#.
• why do i get Segmentation fault (core dumped) error here?

  while trying to regenerate the function strrchr i get this error, can someone help me understand this part?

  #include <stdio.h>
  
  char  *ft_strrchr(const char *s, int c)
  {
    int i;
    char *ptr;
    ptr = NULL;
    i = 0;
    while (*s)
    {
        if (*(s + i) == (const char)c)
        {
            ptr = ((char*)(s + i));
        }
        ++i;
    }
    return (ptr);
  }
  
  int main()
  {
      const char *tx = "test a test a test";
      int a = 'a';
      char *ptr = ft_strrchr(tx,a);
      printf("%c",*ptr);
  
      return 0;
  

  }