So i wrote a very simple program which includes a linked list,
the nodes within the list are dynamically allocated using malloc(), the program had 2 functions, add a new node to the list and print the nodes in the list.
Every time i added more than 2 nodes to the list(including the start node) and used the print function the program crashed.
With some if and print statements i found that the third (or which ever was last) node's *next was not NULL even though obviously it was not pointing at anything since it was the last node in the list.
The program crashed because there is a while loop that depended on that pointer being NULL to stop.
Anyway, changing the size of the array to 12 fixed the problem.
My question is why? I included the entire program if your interested
but it's kinda messy.
Code:typedef struct example{ char array[52]; struct example *next; }typeExample;
Code:#include <stdio.h> #include <string.h> #include <stdlib.h> //http://cboard.cprogramming.com/c-programming/167968-please-need-help-linked-list.html#post1239483 typedef struct LSexample{ char name[12]; // name was too big that was the problem float decimals; struct LSexample *forward; }typeLS; typeLS *returnPointerToAllocatedMemory(typeLS *MainPointers){ char UserInput5[16]; fgets(UserInput5, 15,stdin); typeLS *PointertoAllocatedMemory = malloc(sizeof(typeLS)); sscanf(UserInput5,"%s %f",PointertoAllocatedMemory->name,&PointertoAllocatedMemory->decimals ); printf("Name:%s float:%f\n",PointertoAllocatedMemory->name,PointertoAllocatedMemory->decimals); if(MainPointers != NULL){//if there is somethign behind then set // whats behind pointer to point at the newly created structure MainPointers->forward = PointertoAllocatedMemory;//mainpointers is the previous structure // if there isn't one it will be NULL } return PointertoAllocatedMemory; } void cleanUp(typeLS *FirstStructure1){ typeLS *freeThisAllocatedMemory = NULL; typeLS *HoldPointerForward = NULL; freeThisAllocatedMemory = FirstStructure1; while(freeThisAllocatedMemory != NULL){// if ? REALLY? LOOOOOOOL printf("Free name:%s float %f\n",freeThisAllocatedMemory->name,freeThisAllocatedMemory->decimals); HoldPointerForward = freeThisAllocatedMemory->forward; //if ->forward was bellow free(freeThisAllocatedMemory); //remember its cleaning the pointer not the struct freeThisAllocatedMemory = HoldPointerForward; //i mean here, then the cleaned pointer woudl get dirty again } } void printfunc(typeLS *FSpointer){ typeLS *holder3 = FSpointer; while(holder3 != NULL){ printf("name:%s float:%f\n",holder3->name,holder3->decimals); holder3 = holder3->forward; if(holder3 != NULL){ } } } int main(){ typeLS *Firststructure = NULL;//this pointer will point at the first structure in the list typeLS *holderr = NULL; //this pointer will point at multiple things which is the trick of this logic char UserInput[16]; char translation[16]; while(fgets(UserInput, 15,stdin)){ sscanf(UserInput,"%s",translation); if(strncmp(translation, "add",3)==0){ if(Firststructure == NULL){ Firststructure = returnPointerToAllocatedMemory(NULL); holderr = Firststructure; }else{ holderr = returnPointerToAllocatedMemory(holderr); } }else if(strncmp(translation, "print",5)==0){ printf("Printing...\n"); printfunc(Firststructure); }else if(strncmp(translation, "quit",4)==0){ printf("Breaking...\n"); break; } } cleanUp(Firststructure); return 0; }
Originally Posted by Anonymouss
