C pointers in linked list [closed] - c

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Closed 10 years ago.
Doing a homework and I'm having problems with, what I believe, pointers.
The assignment consists in the following:
I have a txt file where each line as a name and a password.
thisismyname:thisismypassword
I have to read this data, process it into struct linked list, run all the list and send the password to a brute-force algorithm. This algorithm, after finding the pass, should write the pass on the struct. In the end, I should run the list and write the data to a txt file
My problem is when I find the password. It is not storing its value in the struct. At the end I can read the data, I can see that the brute-force is working but at the end, I'm only managing to write the name and pass to file. The unencrypted pass is being written as NULL so I believe is a pointer problem.
This is the code (Removed all the things that I believe are irrelevant):
typedef struct p {
char *name;
char *pass;
char *pass_desenc;
struct p *next_person;
} person;
typedef struct n {
int a;
int b;
} numbers;
int readFile(person **people) {
FILE * fp;
char line[100];
if ((fp = fopen(STUDENTS_FILE, "r")) != NULL) {
while (fgets(line, sizeof (line), fp) != NULL) {
person *p;
char email[27] = "";
char password[14] = "";
char *change = strchr(line, '\n');
if (change != NULL)
*change = '\0';
/* Gets email*/
strncpy(email, line, 26);
email[27] = '\0';
/* Gets pass*/
strncpy(password, line + 27, 14);
password[14] = '\0';
p = (person*) malloc(sizeof (person));
if (p == NULL) {
return -1;
}
p->name = (char*) malloc(strlen(email));
if (p->name == NULL) {
return -1;
}
sprintf(p->name, "%s", email);
p->name[strlen(email)] = '\0';
p->pass = (char*) malloc(strlen(password));
if (p->pass == NULL) {
return -1;
}
sprintf(p->pass, "%s", password);
p->pass[strlen(password)] = '\0';
p->next_person = (*people);
(*people) = p;
countPeople++;
}
fclose(fp);
return 0;
}
return -1;
}
void fmaps(int id, numbers pass_range, person *people) {
/*This function will run all my list and try to uncrypt pass by pass.
On the brute-force pass in unencrypted and when it return to this function, I can print the data.
*/
while (people != NULL && j > 0) {
for (i = 1; i <= PASS_SIZE && notFound == 1; i++) {
notFound = bruteForce(i, people, &total_pass);
}
notFound = 1;
count = count + total_pass;
printf("#####Email: %s Pass: %s PassDesenq: %s \n", people->name, people->pass, people->pass_desenc);
people = people->next_person;
j--;
}
}
void fcontrol(int n, person *people) {
/*This function should write the data to a file
I can see that all data is written as expected but people->pass_desenc is writing/printing NULL
*/
if ((fp = fopen(STUDENTS_LOG_FILE, "a+")) != NULL) {
while (people != NULL) {
printf("#####1111Email: %s Pass: %s PassDesenq: %s \n", people->name, people->pass, people->pass_desenc);
fprintf(fp, "%d%d%d%d%d%d:grupo%d:%s:%s\n", tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec, 1, people->name, people->pass_desenc);
people = people->next_person;
}
}
fclose(fp);
}
int main() {
/*Struct*/
person *people = NULL;
if (readFile(&people)) {
printf("Error reading file!\n");
return 0;
}
/*Function to send data to brute-force*/
fmaps(i, pass_range, people);
/*After all data is processed, this function writes the data to a file*/
fcontrol(NR_PROC, people);
destroyList(&people);
return 0;
}
int bruteForce(int size, person *people, int *total_pass) {
int i;
char *pass_enc;
int *entry = (int*) malloc(sizeof (size));
char pass[50];
char temp;
pass[0] = '\0';
for (i = 0; i < size; i++) {
entry[i] = 0;
}
do {
for (i = 0; i < size; i++) {
temp = (char) (letters[entry[i]]);
append(pass, temp);
}
(*total_pass)++;
/*Compare pass with test*/
pass_enc = crypt(pass, salt);
if (strcmp(pass_enc, people->pass) == 0) {
people->pass_desenc = (char*) malloc(strlen(pass));
if (people->pass_desenc == NULL) {
return -1;
}
sprintf(people->pass_desenc, "%s", pass);
people->pass_desenc[strlen(pass)] = '\0';
return 0;
}
pass[0] = '\0';
for (i = 0; i < size && ++entry[i] == nbletters; i++) {
entry[i] = 0;
}
} while (i < size);
free(entry);
return 1;
}
void append(char *s, char c) {
int len = strlen(s);
s[len] = c;
s[len + 1] = '\0';
}
void destroyList(person **people) {
person *aux;
printf("\nList is being destroyed.");
while (*people != NULL) {
aux = *people;
*people = (*people)->next_person;
free(aux);
printf(".");
}
printf("\nList destroyed.\n");
}
I believe that the changes being made in fmaps are local and are not passing to main.
Any help is appreciated...

Answer 1

This is how you could code the file reader/parser. It avoids str[n]cpy(), and does all string operations using memcpy() + the offsets + sizes. (which need to be correct in both cases, obviously)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
typedef struct p {
char *name;
char *pass;
// char *pass_desenc;
struct p *next;
} person;
#define STUDENTS_FILE "students.dat"
unsigned countPeople = 0;
int readFile(person **people) {
FILE * fp;
char line[100];
size_t len, pos;
fp = fopen(STUDENTS_FILE, "r");
if (!fp) {
fprintf(stderr, "Could not open %s:%s\n"
, STUDENTS_FILE, strerror(errno));
return -1;
}
while ( fgets(line, sizeof line, fp) ) {
person *p;
len = strlen(line);
/* remove trailng '\n', adjusting the length */
while (len && line[len-1] == '\n') line[--len] = 0;
/* Ignore empty lines */
if ( !len ) continue;
/* Library function to count the number of characters in the first argument
** *not* present in the second argument.
** This is more or less equivalent to strtok(), but
** 1) it doen not modify the string,
** 2) it returns a size_t instead of a pointer.
*/
pos = strcspn(line, ":" );
/* Ignore lines that don't have a colon */
if (line[pos] != ':') continue;
p = malloc(sizeof *p);
if ( !p ) { fclose(fp); return -2; }
p->next = NULL;
p->name = malloc(1+pos);
if ( !p->name ) { fclose(fp); return -3; } /* this could leak p ... */
memcpy(p->name, line, pos-1);
p->name[pos] = 0;
p->pass = malloc(len-pos);
if ( !p->pass ) {fclose(fp); return -4; } /* this could leak p and p->name */
memcpy(p->pass, line+pos+1, len-pos);
/* Instead of pushing (which would reverse the order of the LL)
** , we append at the tail of the LL, keeping the original order.
*/
*people = p;
people = &p->next ;
countPeople++;
}
fclose(fp);
return 0;
}