I am making a program using dynamic memory and was able to successfully code it going into the file, but need help reading it back, I am stuck in the function Load.
Just wondering how you would read it back in using no arrays, any ideas? For now I will assume the words input have no spaces for convenience.Code:#include <stdlib.h> #include <stdio.h> #include <string.h> #include <ctype.h> struct point { int x; //point x int y; //point y char label[21]; //label of 2 points struct point *ptrNext; // self referential pointer }; //Global: struct point *ptrFirst = NULL;//empty list (ptrFirst is the head of the list struct point *ptrLast = NULL;//empty list (ptrLast is the tail of the list) //Prototypes: struct point *CreatePoint(); int isEmptyList(struct point *ptrF); void PrintList(struct point *ptr); void ResetList(); struct point *AddToBeginning(struct point *ptrNew); struct point *AddToEnd(struct point *ptrNew); struct point* InputRecord(struct point *ptrNew); // used by Add to interactively get the values from the user void Save(const char* filename); void Load(const char* filename); int count=0; int main() { int run=1; int input=1; int result=0; while(run==1) { printf( "1. Add a point at the END of the list.\n" "2. Add a point at the BEGINNING of the list.\n" "3. Is the list empty?\n" "4. Erase all points from the list (reset).\n" "5. Display the list.\n" "6. Save the list to a sequential file (reset/replace file contents)\n" "7. Read the list back from a sequential file\n" "(reset/replace current memory content)\n" "0. Exit\n\n" ); scanf("%d", &input); switch(input) { case 0: { ResetList(ptrFirst); run = 0; break; } case 1: { AddToEnd(InputRecord(CreatePoint())); break; } case 2: { AddToBeginning(InputRecord(CreatePoint())); break; } case 3: { if(isEmptyList(ptrFirst)==0) printf("The list is empty\n\n"); else printf("The list is not empty\n\n"); break; } case 4: { ResetList(ptrFirst); break; } case 5: { PrintList(ptrFirst); break; } case 6: { result=Save("data.dat"); break; } case 7: { result=Load("data.dat"); break; } default: { printf("Invalid entry, try again\n\n"); break; } } } } //CreatePoint creates using dynamic memory allocation a new record of type point //Input: assumes enough dynamic memory is available //Output: returns a pointer to the enw point, or NULL if not enough memory struct point *CreatePoint() { return (struct point *)(malloc(sizeof(struct point))); } //isEmptyList checks if the list is empty int isEmptyList(struct point *ptrF) { if(ptrF==NULL) return 0; else return 1; } //PrintList will print out the contents of the list void PrintList(struct point *ptr) { if(ptr!=NULL) { printf("x: %d\ny: %d\nlabel: %s\n\n",ptr->x,ptr->y,ptr->label); PrintList(ptr->ptrNext); } } //ResetList will empty or free() the contents of the list void ResetList() { struct point *ptrDel=ptrFirst; while(ptrFirst!=NULL) { ptrDel=ptrFirst; ptrFirst=ptrFirst->ptrNext; free(ptrDel); } } //AddToBeginning adds a new record to the beginning of the list //Input: assumes a valid record is given and initialized properly //Output: adds the record to the beginning, returns a pointer to that record struct point* AddToBeginning(struct point *ptrNew) { //case 1: ptrNew is not valid(ie. NULL - nothing to add!) if(ptrNew==NULL) return NULL; //case 2: add the record to an empty list if(ptrFirst==NULL) { ptrFirst=ptrNew; ptrLast=ptrNew; } //case 3: you are adding new record to an existing list else { ptrNew->ptrNext=ptrFirst; ptrFirst=ptrNew; } return ptrNew; } //AddToEnd will add a point to the end of the list struct point *AddToEnd(struct point *ptrNew) { //case 1: ptrNew is not valid(ie. NULL - nothing to add!) if(ptrNew==NULL) return NULL; //case 2: add the record to an empty list if(ptrFirst==NULL) { ptrFirst=ptrNew; ptrLast=ptrNew; } //case 3: add the record to an existing list else { ptrLast->ptrNext = ptrNew; ptrLast = ptrNew; } } //InputRecord sets the initial values of a new record //Input: a pointer to an existing record //Output: sets the int value to a value from the keyboard, and null to all pointers // and returns the same pointer to that initialized record struct point* InputRecord(struct point *ptrNew) { if(ptrNew==NULL) //fail-safe: check for valid pointer return NULL; printf("Please enter the data for x and y:\n"); scanf("%d%d", &ptrNew->x,&ptrNew->y); printf("Please enter the label for the data:\n"); scanf("%s", ptrNew->label); ptrNew->ptrNext=NULL; return ptrNew; } int Save(const char* filename) { count=0; FILE* outfile; struct point *ptrCurrent = ptrFirst; if(isEmptyList(ptrFirst)==0) return 0; outfile = fopen(filename, "w"); if (outfile == NULL) return 0; while(ptrCurrent != NULL) { count++; fprintf(outfile, "%d %d %s",ptrCurrent->x,ptrCurrent->y,ptrCurrent->label); if(ptrCurrent->ptrNext != NULL) fprintf(outfile, "\n"); ptrCurrent=ptrCurrent->ptrNext; } fclose(outfile); } int Load(const char* filename) { FILE* infile; struct point *ptrNew = NULL; infile = fopen(filename, "r"); if (infile == NULL) return 0; // ready to read from file, reset (clear) current list! ResetList(ptrFirst); while(!feof(infile)) { ptrNew = (struct point *) (malloc(sizeof(struct point))); if (ptrNew == NULL) break; //STUCK HERE }
Originally Posted by JamesD
