See on osaline lahendus realloc() tunnitööle. NB! Jälgi kommentaare, mitmetes kohtades on vaja teha täiendusi.
**ptr: lahendus, mis edastab struktuuri topeltviidana ja tagastab ridade arvu*ptr: Lahendus, mis edastab ridade arvu viida abil ning tagastab viida andmestruktuurile
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#ifndef REALLOC_EXAMPLE_H #define REALLOC_EXAMPLE_H #define LEN_CUR_CODE 4 #define BUF_LEN 128 #define DEFAULT_INPUT_FILE "candidates.txt" typedef struct { int index; char *fName; char *lName; char curriculum[LEN_CUR_CODE + 1]; float points; } Person; int ReadList(Person **ppStudentData, char *fileName); void Output(Person *candidates, int n); #endif //REALLOC_EXAMPLE_H |
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/** * File: realloc_example.c * Author: Risto Heinsar * Created: 19.03.2014 * Edited: 02.04.2024 * * Description: The following code will demonstrate how to properly use realloc * to expand the memory that's already been allocated. * The file is a part of the IAX0584 lab task and provided as a * partial lab solution. It implements the less efficient (n + 1) * expansion strategy which is considered slow in real world. */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include "realloc_example.h" int main(void) { char fileName[] = DEFAULT_INPUT_FILE; Person *list = NULL; // nothing here at present // read the file int candidateCnt = ReadList(&list, fileName); Output(list, candidateCnt); // NB! The sample code does not include freeing the memory. // Everything that you allocate for must be freed before exiting the program! return EXIT_SUCCESS; } /** * Description: Function to read data from a file. During this, a dynamic * struct array will be created and expanded using realloc() * Parameters: Double pointer a struct, address of the allocated array will * be stored there. NB! The memory comes from the heap! * Pointer to a string with the file name * Return value: Returns an integer with the number of lines read from the file * Prerequisites: Datafile fields are separated with either a space * or a line change, without faulty data, max length of a string * is up to (LEN_NAME_MAX - 1) and no spaces in strings. */ int ReadList(Person **ppStudentData, char *fileName) { // Opening the file and checking if it opened FILE *fp = fopen(fileName, "r"); if (fp == NULL) { perror("Error opening input file:"); exit(EXIT_FAILURE); } // Main data pointer that's used locally Person *pData = NULL; // Temporary buffers for data during reading char bufFName[BUF_LEN], bufLName[BUF_LEN], bufCurrCode[BUF_LEN]; int bufInd; float bufPoints; // initialize the line count to 0 - nothing read yet int count = 0; // start by reading one line at a time into the buffers (no memory yet) while (fscanf(fp, "%d %s %s %s %f", &bufInd, bufFName, bufLName, bufCurrCode, &bufPoints) == 5) { // if a line was successfully read, expanding the memory by 1. Using a // temporary pointer to avoid losing memory address when realloc fails // during reading (returns NULL, old pointer valid) Person *pTemp = realloc(pData, sizeof(Person) * (unsigned)(count + 1)); // Check if it failed if (pTemp == NULL) { // TODO: Error behavior! // I.e. if you want to free everything and exit, you should free: // - all the first names already allocated // - all the last names allocated // - the struct itself // then close the file and exit fclose(fp); exit(EXIT_FAILURE); } // Make both pointers point at the memory location pData = pTemp; // Copy data from buffers to the struct array // Now allocate + copy data for the string buffers // Note 1: Both pData[i].member or (pData + i)->member can be used // Note 2: strdup() combines strlen, malloc and strcpy (pData + count)->fName = strdup(bufFName); if ((pData + count)->fName == NULL) { // TODO: error behavior here } // numbers can be copied directly, there already is memory in the struct (pData + count)->points = bufPoints; // another line successfully read count++; } // using the dbl pointer to make sure main() knows where my struct array is *ppStudentData = pData; // close the file fclose(fp); // and return the number of lines read return count; } /** * Description: Prints out the list of candidates who applied, one per line. * Parameters: candidateList - pointer to the list of candidates * n - number of candidates in the list * Return value: none */ void Output(Person *candidates, int n) { printf("The candidates are:\n"); for (int i = 0; i < n; i++) { // the fields which were incomplete are not printed at this point. printf("%d %s <last name> <curriculum> %.2f\n", (candidates + i)->index, (candidates + i)->fName, (candidates + i)->points); } } |
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#ifndef REALLOC_EXAMPLE_H #define REALLOC_EXAMPLE_H #define LEN_CUR_CODE 4 #define BUF_LEN 128 #define DEFAULT_INPUT_FILE "candidates.txt" typedef struct { int index; char *fName; char *lName; char curriculum[LEN_CUR_CODE + 1]; float points; } Person; Person * ReadList(int *cnt, char *fileName); void Output(Person *candidates, int n); #endif |
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/** * File: realloc_example.c * Author: Risto Heinsar * Created: 19.03.2014 * Edited: 02.04.2024 * * Description: The following code will demonstrate how to properly use realloc * to expand the memory that's already been allocated. * The file is a part of the IAX0584 lab task and provided as a * partial lab solution. It implements the less efficient (n + 1) * expansion strategy which is considered slow in real world. */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include "realloc_example.h" int main(void) { char fileName[] = DEFAULT_INPUT_FILE; int total; // read the file Person *candidates = ReadList(&total, fileName); Output(candidates, total); // NB! The sample code does not include freeing the memory. // Everything that you allocate for must be freed before exiting the program! return EXIT_SUCCESS; } /** * Description: Function to read data from a file. During this, a dynamic * struct array will be created and expanded using realloc() * Pointer to a string with the file name * Parameters: Pointer to an integer where to store the candidate count * Pointer to a string with the file name * Return value: Returns the structure pointer where the memory was allocated * and data stored at. * Prerequisites: Datafile fields are separated with either a space * or a line change, without faulty data, max length of a string * is up to (LEN_NAME_MAX - 1) and no spaces in strings. */ Person * ReadList(int *cnt, char *fileName) { // Opening the file and checking if it opened FILE *fp = fopen(fileName, "r"); if (fp == NULL) { perror("Error opening input file:"); exit(EXIT_FAILURE); } // Main data pointer that's used locally Person *pData = NULL; // Temporary buffers for data during reading char bufFName[BUF_LEN], bufLName[BUF_LEN], bufCurrCode[BUF_LEN]; int bufInd; float bufPoints; // Initialize the line count to 0 - nothing read yet int count = 0; // start by reading one line at a time into the buffers (no memory yet) while (fscanf(fp, "%d %s %s %s %f", &bufInd, bufFName, bufLName, bufCurrCode, &bufPoints) == 5) { // if a line was successfully read, expanding the memory by 1. Using a // temporary pointer to avoid losing memory address when realloc fails // during reading (returns NULL, old pointer valid) Person *pTemp = realloc(pData, sizeof(Person) * (unsigned)(count + 1)); // Check if it failed if (pTemp == NULL) { // TODO: Error behavior! // I.e. if you want to free everything and exit, you should free: // - all the first names already allocated // - all the last names allocated // - the struct itself // then close the file and exit fclose(fp); exit(EXIT_FAILURE); } // Make both pointers point at the memory location pData = pTemp; // Copy data from buffers to the struct array // Now allocate + copy data for the string buffers // Note 1: Both pData[i].member or (pData + i)->member can be used // Note 2: strdup() combines strlen, malloc and strcpy (pData + count)->fName = strdup(bufFName); if ((pData + count)->fName == NULL) { // TODO: error behavior here } // numbers can be copied directly, there already is memory in the struct (pData + count)->points = bufPoints; // another line successfully read count++; } // using a pointer to store the number of lines that were read *cnt = count; // now just close the file fclose(fp); // and return the pointer to the struct array we just allocated return pData; } /** * Description: Prints out the list of candidates who applied, one per line. * Parameters: candidateList - pointer to the list of candidates * n - number of candidates in the list * Return value: none */ void Output(Person *candidates, int n) { printf("The candidates are:\n"); for (int i = 0; i < n; i++) { // the fields which were incomplete are not printed at this point. printf("%d %s <last name> <curriculum> %.2f\n", (candidates + i)->index, (candidates + i)->fName, (candidates + i)->points); } } |