Scanf Validation - c

Question

Can someone help me validate the inputs for the Scanf's i have below. I want the programme to ask for the data to be re-entered if the Scanf's are within an incorrect range or not an interger. I put in a do while loop before with an if statement but when i compiled it the first printf and scanf just looped
#include <stdio.h>
#include <stdlib.h>
int MenuLoop = 0;
int MaxPackets = 4;
int currentPackets= 0;
int menu;
/*********************************************************
* Node to represent a Cat which includes a link reference*
* a link list of nodes with a pointer to a Cat Struct *
* would be better but this is for illustartion only! *
**********************************************************/
struct Packet {
int Source;
int Destination;
int Type;
int Port;
char *Data;
struct Packet *next; // Link to next Cat
};
typedef struct Packet node; // Removes the need to constantly refer to struct
/*********************************************************
* Stubs to fully declared functions below *
**********************************************************/
void outputPackets(node **head);
void push(node **head, node **aPacket);
node* pop(node **head);
void AddPacket();
void AddPacket();
void SavePacket();
void ShowCurrent();
void ExitProgramme();
main() {
do{
Menu();
} while(menu<4);
}
void AddPacket(){
int option;
/*********************************************************
* pointers for the link list and the temporary P to *
* insert into the list *
**********************************************************/
node *pPacket, *pHead = NULL;
/*********************************************************
* Create a cat and also check the HEAP had room for it *
**********************************************************/
pPacket = (node *)malloc(sizeof(node));
if (pPacket == NULL)
{
printf("Error: Out of Memory\n");
exit(1);
}
currentPackets++;
printf("Enter Source Number between 1-1024:\n");
scanf("%i", &pPacket->Source);
printf("Enter Destination Number between 1-1024:\n");
scanf("%i", &pPacket->Destination);
printf("Enter Type Number between 0-10:\n");
scanf("%i", &pPacket->Type);
printf("Enter Port Number between 1-1024:\n");
scanf("%i", &pPacket->Port);
printf("Enter Data Numberbetween 1-50:\n");
scanf("%s", &pPacket->Data);
printf("Do you want to Enter another Packet?");
pPacket->next = NULL;
/*********************************************************
* Push the Cat onto the selected Link List, the function *
* is written so the program will support multiple link *
* list if additional 'pHead' pointers are created. *
* Who says you cannot herd cats! *
**********************************************************
* NOTE: The push parameters are using references to the *
* pointers to get round the pass by value problem caused *
* by the way C handles parameters that need to be *
* modified *
**********************************************************/
push(&pHead, &pPacket);
pPacket = (node *)malloc(sizeof(node));
if (pPacket == NULL)
{
printf("Error: Out of Memory\n");
exit(1);
}
outputPackets(&pHead);
/*********************************************************
* Display the Link List 'pHead' is passed as a reference *
**********************************************************/
return 0;
do{
if(currentPackets == MaxPackets);
{
printf("Packet limit reached please save\n");
}
}while(currentPackets<MaxPackets);
return 0;
}
void outputPackets(node **head)
{
/*********************************************************
* Copy Node pointer so as not to overwrite the pHead *
* pointer *
**********************************************************/
node *pos = *head;
/*********************************************************
* Walk the list by following the next pointer *
**********************************************************/
while(pos != NULL) {
printf("Source: %.4i Destination: %.4i Type: %.4i Port: %.4i \n", pos->Source, pos->Destination, pos->Type, pos->Port);
pos = pos->next ;
}
printf("End of List\n\n");
}
void push(node **head, node **aPacket)
{
/*********************************************************
* Add the cat to the head of the list (*aCat) allows the *
* dereferencing of the pointer to a pointer *
**********************************************************/
(*aPacket)->next = *head;
*head = *aPacket;
}
node *pop(node **head)
{
/*********************************************************
* Walk the link list to the last item keeping track of *
* the previous. when you get to the end move the end *
* and spit out the last Cat in the list *
**********************************************************/
node *curr = *head;
node *pos = NULL;
if (curr == NULL)
{
return NULL;
} else {
while (curr->next != NULL)
{
pos = curr;
curr = curr->next;
}
if (pos != NULL) // If there are more cats move the reference
{
pos->next = NULL;
} else { // No Cats left then set the header to NULL (Empty list)
*head = NULL;
}
}
return curr;
}
void SavePacket(){
FILE *inFile ;
char inFileName[10] = { '\0' } ;
printf("Input file name : ") ;
scanf("%s", inFileName) ;
//Open file
inFile = fopen(inFileName, "w+");
if (!inFile)
{
fprintf(stderr, "Unable to open file %s", &inFile);
exit(0);
}
//fprintf(inFile, "Source: %i Destination: %i Type: %i Port: %i \n", pos->Source, pos->Destination, pos->Type, pos->Port);
fclose(inFile);
}
void ShowCurrent(){
}
void ExitProgramme(){}
void Menu(){
printf("********Welcome****** \n");
printf("Creator Ben Armstrong.\n\n");
printf("*Please Choose an option*\n");
printf("1. Add a new packet\n");
printf("2. Save current packet to file\n");
printf("3. Show current list of packets\n");
printf("4. Exit\n");
scanf("%i", &menu);
switch(menu)
{
case 1:
AddPacket();
break;
case 2:
SavePacket();
break;
case 3 :
ShowCurrent();
break;
case 4 :
ExitProgramme();
break;
}
}
This is my full code as u can see im trying to implement a link list which the data has to be validated for

Answer 1

Use the following macro
#define SCAN_ONEENTRY_WITHCHECK(FORM,X,COND) \
do {\
char tmp;\
while(((scanf(" "FORM"%c",X,&tmp)!=2 || !isspace(tmp)) && !scanf("%*[^\n]"))\
|| !(COND)) {\
printf("Invalid input, please enter again: ");\
}\
} while(0)
You find in this topic the macro explaination
Example of using it :
int main()
{
.......
printf("Enter Source Number between 1-1024:\n");
SCAN_ONEENTRY_WITHCHECK("%i", &pPacket->Source, (pPacket->Source>=1 && pPacket->Source<=1024);
printf("Enter Destination Number between 1-1024:\n");
SCAN_ONEENTRY_WITHCHECK("%i", &pPacket->Destination, (pPacket->Destination>=1 && pPacket->Destination<=1024);
printf("Enter Type Number between 0-10:\n");
SCAN_ONEENTRY_WITHCHECK("%i", &pPacket->Type, (pPacket->Type>=0 && pPacket->Type<=10);
printf("Enter Port Number between 1-1024:\n");
SCAN_ONEENTRY_WITHCHECK("%i", &pPacket->Port, (pPacket->Port>=1 && pPacket->Port<=1024);
printf("Enter Data Numberbetween 1-50:\n");
SCAN_ONEENTRY_WITHCHECK("%i", &pPacket->Data, (pPacket->Data>=1 && pPacket->Data<=50);
}

Answer 2

Here is one approach using strtol:
#include <stdlib.h>
#include <stdio.h>
struct Packet {
int Source;
int Destination;
int Type;
int Port;
int Data;
};
void func(struct Packet *pPacket) {
char entry[100];
int i;
char *tail;
do {
printf("Enter Source Number between 1-1024:\n");
scanf("%99s", entry);
i = strtol(entry, &tail, 0);
} while (*tail || i < 1 || i > 1024);
pPacket->Source = i;
}
int main(int argc, char* argv[])
{
struct Packet pPacket;
func(&pPacket);
printf("pPacket->Source is now %i.\n", pPacket.Source);
return 0;
}