Program execution stop at scanf???

Question

main.c (with all the headers like stdio, stdlib, etc):

int main()
{
int input;

while(1)
{
    printf("\n");
    printf("\n1. Add new node");
    printf("\n2. Delete existing node");
    printf("\n3. Print all data");
    printf("\n4. Exit");
    printf("Enter your option -> ");
    scanf("%d", &input);

    string key = "";
    string tempKey = "";
    string tempValue = "";
    Node newNode;
    Node temp;
    switch (input) {
        case 1:
            printf("\nEnter a key: ");
            scanf("%s", tempKey);
            printf("\nEnter a value: ");
            scanf("%s", tempValue);          //execution ternimates here

            newNode.key = tempKey;
            newNode.value = tempValue;

            AddNode(newNode);
            break;
        case 2:
            printf("\nEnter the key of the node: ");
            scanf("%s", key);
            temp = GetNode(key);
            DeleteNode(temp);
            break;
        case 3:
            printf("\n");
            PrintAllNodes();
            break;
        case 4:
            exit(0);
            break;
        default:
            printf("\nWrong option chosen!\n");
            break;
    }
}

return 0;
}

storage.h:

#ifndef DATABASEIO_H_
#define DATABASEIO_H_

//typedefs
typedef char *string;

/*
 * main struct with key, value,
 * and pointer to next struct
 * Also typedefs Node and NodePtr
 */
typedef struct Node {
    string key;
string value;
struct Node *next;
} Node, *NodePtr;

//Function Prototypes
void AddNode(Node node);
void DeleteNode(Node node);
Node GetNode(string key);
void PrintAllNodes();

#endif /* DATABASEIO_H_ */

I am using Eclipse CDT, and when I enter 1, then I enter a key. Then the console says . I used gdb and got this error:

Program received signal SIGSEGV, Segmentation fault.
0x00177024 in _IO_vfscanf () from /lib/tls/i686/cmov/libc.so.6

Any ideas why?

Answer 1

Hmm, are you sure that scanf can use the provided string to store the data?

I'd try to use a char buffer that is large enough or switch to real C++ functions to read input.

Answer 2

you should allocate enough memory for your strings (typedef char* string) to read into with scanf()

Answer 3

You have to allocate all the storage that scanf() is going to use before you call it; scanf() does not allocate storage. Your strings are empty; there is minimal storage allocated for the values. Entering any extra data is a disaster.

Plus, scanf() expects a character pointer, not a string reference or value - because it is a variadic function, there is only a limited amount of warning that the compiler can do.

Answer 4

• Like Jonathan & Patrick said, Allocate the memory first and then pass the pointers/arrays to scanf.

//Change the value here to change the size of Ur strings (char-arrays actually)
#define MAX_LENGTH 20

char key[MAX_LENGTH];

char tempKey[MAX_LENGTH];

char tempValue[MAX_LENGTH];

You might also want to checkout a small walkthrough on gdb that i have over here:

> 2600Hertz/Hacking-into-any-executable-using-gdb/

GoodLUCK!!

CVS @ 2600Hertz