Why do my functions crash the programme? - c

Question

#include <stdio.h>
#include <stdlib.h>
struct packets
{
int source, destination, type, port;
char data[50];
};
int addpacket(int *, struct packets *);
void listpackets(int , struct packets *);
void save(int, struct packets *);
int main()
{
struct packets *info;
char choice;
int records = 0;
info = malloc(sizeof(struct packets));
do
{
puts("\n1. Add Packets\n"); //Menu with list of options.
puts("\n2. List all saved packets\n");
puts("\n3. Save packets\n");
puts("\n4. Clear all packet information\n");
puts("\nx. Exit the programme\n");
printf("\nPlease select your option: \n");
scanf("%c", &choice); //Reading the menu option entered.
if(choice == '\n') //if the choice is the new line character read again.
scanf("%c", &choice);
switch (choice)
{
case '1': system("cls"); //Clears the screen
puts("\nYou have selected to Add packet information, follow on-screen instructions\n"); records = addpacket(&records, info); //calls function "addpacket" and sents a copy of records and pointer to struct info.
break;
case '2': system("cls"); //clears the screen
puts("\nAll packet information will now be displayed on the screen\n"); listpackets(records, info);
break;
case '3': system("cls"); //clears the screen
puts("\nAll packet information will now be saved\n"); save(records, info);
break;
case '4': system("cls"); //clears the screen
puts("\nAll packet information will now be deleted\n");
break;
case 'x': puts("\nThe proframme will now close, Goodbye!\n"); //closes the programme.
break;
default : puts("\nIncorrect option, please select from menu\n"); //used if none of the menu options have been selected.
break;
}
}while (choice != 'x'); //The programme will run until the "x" option is entered at the menu.
return 0;
}
int addpacket(int *recCount, struct packets *info)
{
int validation = 0;
int stringlength = 0;
int i = 0;
char datatest[50];
do{
printf("\nPlease enter the source address: \n");
if (scanf("%i", &info[*recCount].source) == 1)
{
validation = 1;
}
else{
validation = 0;
getchar();
puts("\nThis is not a valid source address!\n");
}
}while (validation != 1);
printf("\nPlease enter destination address: \n");
scanf("%i", &info[*recCount].destination); //pointer to the destination address.
printf("\nPlease enter type: \n");
scanf("%i", &info[*recCount].type); // pointer to the address of the type.
printf("\nPlease enter the port: \n");
scanf("%i", &info[*recCount].port); //pointer to the port address.
printf("\nPlease enter data: \n");
scanf("%s", info[*recCount].data); //pointer to the data address.
*recCount ++; //adding one to record count
return *recCount; // returning the record count which will the be copied into records in main.
}
void listpackets(int records, struct packets *info)
{
int i;
for (i=0; i<records; i++){
printf("\nSource address: %i\n", info[i].source); //Displays the source address.
printf("\nDestination address: %i\n", info[i].destination); //Displays the destination address.
printf("\nType: %i\n", info[i].type); //Displays the type.
printf("\nPort: %i\n", info[i].port); //displays the port.
printf("\nData: %s\n", info[i].data); //displays the data information.
}
}
void save(int records, struct packets *info)
{
FILE *savedfile;
char filename[30] = { '\0'}; //this is where the file name will be stored.
int i;
printf("\nPlease enter a filename: \n");
scanf("%s", filename);
if ((savedfile = fopen(filename, "w")) == NULL)
{
printf("\n%s could not be opened\n", filename);
exit(1);
}
else
{
for (i=0; i<records; i++)
fprintf(savedfile, "%i %i %i %i %s", info[i].source, info[i].destination, info[i].type, info[i].port, info[i].data);
}
fclose(savedfile);
}
My save and listpacket function crash when i call them. this was working earlier until i introduced malloc into my programme along side some basic input validation. i think this could be an issue with pointers. my programme compiles with no errors/warning so i am stuck with what the problem could be. feel free to try compiling to programme and see what i mean. any help would be greatly appreciated as i am struggling to fix this issue.

Answer 1

You're using malloc() to allocate space for a single struct packets. You later treat your info pointer as if it is an array of records such structures... you're going beyond the boundary of where you have allocated space.
Details on one potential way around (that will auto-grow your array):
// change the signature of addpacket():
int addpacket(int *, struct packets **);
...
// change how add packet gets called:
records = addpacket(&records, &info);
// change addpacket():
int addpacket(int *recCount, struct packets **callerinfo)
{
...
// grow the buffer by one record
*callerinfo = realloc(*callerinfo, (*recCount + 1) * sizeof (**callerinfo));
struct packets *info = *callerinfo; // to avoid changing other code
... no other changes, just the rest of your routine
}
That will come close, of not completely solve it.
The complete program, working for me:
#include <stdio.h>
#include <stdlib.h>
struct packets
{
int source, destination, type, port;
char data[50];
};
int addpacket(int *, struct packets **);
void listpackets(int , struct packets *);
void save(int, struct packets *);
int main()
{
struct packets *info;
char choice;
int records = 0;
info = malloc(sizeof(struct packets));
do
{
puts("\n1. Add Packets\n"); //Menu with list of options.
puts("\n2. List all saved packets\n");
puts("\n3. Save packets\n");
puts("\n4. Clear all packet information\n");
puts("\nx. Exit the programme\n");
printf("\nPlease select your option: \n");
scanf("%c", &choice); //Reading the menu option entered.
if(choice == '\n') //if the choice is the new line character read again.
scanf("%c", &choice);
switch (choice)
{
case '1': system("cls"); //Clears the screen
puts("\nYou have selected to Add packet information, follow on-screen instructions\n"); records = addpacket(&records, &info); //calls function "addpacket" and sents a copy of records and pointer to struct info.
break;
case '2': system("cls"); //clears the screen
puts("\nAll packet information will now be displayed on the screen\n"); listpackets(records, info);
break;
case '3': system("cls"); //clears the screen
puts("\nAll packet information will now be saved\n"); save(records, info);
break;
case '4': system("cls"); //clears the screen
puts("\nAll packet information will now be deleted\n");
break;
case 'x': puts("\nThe proframme will now close, Goodbye!\n"); //closes the programme.
break;
default : puts("\nIncorrect option, please select from menu\n"); //used if none of the menu options have been selected.
break;
}
}while (choice != 'x'); //The programme will run until the "x" option is entered at the menu.
return 0;
}
int addpacket(int *recCount, struct packets **callerinfo)
{
int validation = 0;
int stringlength = 0;
int i = 0;
char datatest[50];
*callerinfo = realloc(*callerinfo, (*recCount + 1) * sizeof (**callerinfo));
struct packets *info = *callerinfo; // to avoid changing other code
do{
printf("\nPlease enter the source address: \n");
if (scanf("%i", &info[*recCount].source) == 1)
{
validation = 1;
}
else{
validation = 0;
getchar();
puts("\nThis is not a valid source address!\n");
}
}while (validation != 1);
printf("\nPlease enter destination address: \n");
scanf("%i", &info[*recCount].destination); //pointer to the destination address.
printf("\nPlease enter type: \n");
scanf("%i", &info[*recCount].type); // pointer to the address of the type.
printf("\nPlease enter the port: \n");
scanf("%i", &info[*recCount].port); //pointer to the port address.
printf("\nPlease enter data: \n");
scanf("%s", info[*recCount].data); //pointer to the data address.
++(*recCount); //adding one to record count
return *recCount; // returning the record count which will the be copied into records in main.
}
void listpackets(int records, struct packets *info)
{
int i;
for (i=0; i<records; i++){
printf("\nSource address: %i\n", info[i].source); //Displays the source address.
printf("\nDestination address: %i\n", info[i].destination); //Displays the destination address.
printf("\nType: %i\n", info[i].type); //Displays the type.
printf("\nPort: %i\n", info[i].port); //displays the port.
printf("\nData: %s\n", info[i].data); //displays the data information.
}
}
void save(int records, struct packets *info)
{
FILE *savedfile;
char filename[30] = { '\0'}; //this is where the file name will be stored.
int i;
printf("\nPlease enter a filename: \n");
scanf("%s", filename);
if ((savedfile = fopen(filename, "w")) == NULL)
{
printf("\n%s could not be opened\n", filename);
exit(1);
}
else
{
for (i=0; i<records; i++)
fprintf(savedfile, "%i %i %i %i %s\n", info[i].source, info[i].destination, info[i].type, info[i].port, info[i].data);
}
fclose(savedfile);
}