I'm currently working on a c library that emulates a stack(using a linked list).
The stack has to be able to manage any data Type.
It also has to be able to write it's contents to a file and then retrieve them. Here is where I'm having problems. When I compare the original stack to the one I stored in the file data is not the same.
Here is the code:
writeRead.c
#include <stdio.h>
#include "stack.h"
#define NODES 3
struct my_data {
int val;
char name[60];
};
int main() {
struct my_stack *s1, *fs1;
struct my_data *data, *data1, *data2;
// Initialize Stack
s1 = my_stack_init(sizeof(struct my_data));
// Initialize data and push to stack
for (int i = 0; i < NODES; i++) {
data = malloc(sizeof(struct my_data)); // We must allocate static memory
data->val = i;
sprintf(data->name, "Value %d", i);
if (my_stack_push(s1, data)) {
puts("Error in my_stack_push()");
exit(1);
}
printf("New node in s1: (%d, %s)\n", data->val, data->name);
}
// Write Stack to file
if (my_stack_write(s1, "/tmp/my_stack.data") == -1) {
puts("Error in my_stack_write (s1)");
exit(1);
}
// Read Stack from file
fs1 = my_stack_read("/tmp/my_stack.data");
if (!fs1) {
puts("Error in my_stack_read (fs1)");
exit(1);
}
// Compare data of stack s1 (memory) and fs1 (file)
while ((data1 = my_stack_pop(s1))) {
printf("FS1 len. %d\n",my_stack_len(fs1));
data2 = my_stack_pop(fs1);
printf("Node of s1: (%d, %s)\t", data1->val, data1->name);
printf("Node of fs1: (%d, %s)\n", data2->val, data2->name);
if (!data2 || data1->val != data2->val || my_strcmp(data1->name, data2->name)) {
printf("Data in s1 and fs1 are not the same.\n (data1->val: %d <> data2->val: %d) o (data1->name: %s <> data2->name: "
"%s)\n",
data1->val, data2->val, data1->name, data2->name);
exit(1);
}
}
return 0;
}
stack.h
#include <fcntl.h> /* Modos de apertura de función open()*/
#include <stdlib.h> /* Funciones malloc(), free(), y valor NULL */
#include <sys/stat.h> /* Permisos función open() */
#include <sys/types.h> /* Definiciones de tipos de datos como size_t*/
#include <unistd.h> /* Funciones read(), write(), close()*/
struct my_stack_node {
void *data;
struct my_stack_node *next;
};
struct my_stack {
int size;
struct my_stack_node *first;
};
int my_strcmp(const char *str1, const char *str2);
struct my_stack *my_stack_init(int size);
int my_stack_push(struct my_stack *stack, void *data);
void *my_stack_pop(struct my_stack *stack);
int my_stack_len(struct my_stack *stack);
struct my_stack *my_stack_read(char *filename);
int my_stack_write(struct my_stack *stack, char *filename);
int my_stack_purge(struct my_stack *stack);
stack.c
#include <stdio.h>
#include "stack.h"
int my_strcmp(const char *str1, const char *str2) {
int restultatCmp = *str1++ - *str2++;
//printf("ResultatCmp : %d \n", restultatCmp);
while(*str1++ && *str2++ && restultatCmp == 0) {
restultatCmp = *str1 - *str2;
}
return restultatCmp;
}
struct my_stack *my_stack_init(int dataSize) {
struct my_stack *stack = malloc(sizeof(struct my_stack));
stack -> first = NULL;
stack -> size = dataSize;
return stack;
}
int my_stack_push(struct my_stack *stack, void *dataIn) {
struct my_stack_node *nodeToPush;
nodeToPush = malloc(sizeof(struct my_stack_node));
if(stack == NULL && sizeof(dataIn)> 0){
printf("Null Stack or data size error.\n");
//la pila debe existir
return -1;
}
else {
nodeToPush -> data = dataIn;
if(stack -> first == NULL) {
nodeToPush -> next = NULL;
stack -> first = nodeToPush;
}
else {
nodeToPush -> next = stack -> first;
stack -> first = nodeToPush;
}
}
return 0;
}
void *my_stack_pop(struct my_stack *stack) {
if(stack -> first == NULL) {
return NULL;
}
struct my_stack_node *nodeToDelete = stack -> first;
void *data = nodeToDelete -> data;
stack -> first = nodeToDelete -> next;
free(nodeToDelete);
return data;
}
int my_stack_len(struct my_stack *stack) {
int numNodes = 0;
struct my_stack_node *currentElement = stack -> first;
while(currentElement != NULL) {
numNodes++;
currentElement = currentElement ->next;
}
return numNodes;
}
void recursiveWrite(struct my_stack_node *nodo, int fileDesc, int sizeData) {
if(nodo ->next != NULL) recursiveWrite(nodo -> next,fileDesc,sizeData);
if(write(fileDesc, nodo -> data, sizeData)== -1){
printf("Error de escritura\n");
return;// error escritura.
}
}
int my_stack_write(struct my_stack *stack, char *filename) {
struct my_stack_node *currentNode = stack -> first;
int fileDesc = open(filename, O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
if(fileDesc == -1) {
return -1; // Error open();
}
if(write(fileDesc, &stack -> size, sizeof(stack -> size)) == -1){
return -1; // Error write();
}
int sizeData = stack -> size;
recursiveWrite(currentNode,fileDesc,sizeData);
close(fileDesc);
return my_stack_len(stack);
}
struct my_stack *my_stack_read(char *filename) {
int fileDesc = open(filename, O_RDONLY, S_IRUSR);
if(fileDesc == -1) {
return NULL; // Error open();
}
char *buffer = malloc(sizeof(int));
int readBytes;
if((readBytes = read(fileDesc, buffer, sizeof(int))) == -1){
printf("Error reading data size.\n");
return NULL;
}
int dataSize = 0;
dataSize = (int) *buffer; // parse data Size from buffer.
struct my_stack *stack;
stack = malloc(sizeof(struct my_stack));
stack = my_stack_init(dataSize); // initialize Stack
buffer = realloc(buffer, stack -> size);
if(buffer == NULL){
return NULL;
}
else{
while(read(fileDesc, buffer, stack -> size) > 0) {
if((my_stack_push(stack,buffer))== -1){
printf("Error en my_stack_read: Push error.\n");
return NULL;
}
}
close(fileDesc);
return stack;
}
}
Sorry for the large code I tried to simplify the example as much as I could.
Output:
New node in s1: (0, Value 0)
New node in s1: (1, Value 1)
New node in s1: (2, Value 2)
FS1 len. 3
Node of s1: (2, Value 2) Node of fs1: (2, Value 2)
FS1 len. 2
Node of s1: (1, Value 1) Node of fs1: (2, Value 2)
Data in s1 and fs1 are not the same.
(data1->val: 1 <> data2->val: 2) o (data1->name: Value 1 <> data2->name: Value 2)
Expected output:
New node in s1: (0, Value 0)
New node in s1: (1, Value 1)
New node in s1: (2, Value 2)
FS1 len. 3
Node of s1: (2, Value 2) Node of fs1: (2, Value 2)
FS1 len. 2
Node of s1: (1, Value 1) Node of fs1: (1, Value 1)
FS1 len. 1
Node of s1: (0, Value 0) Node of fs1: (0, Value 0)
I'm almost sure that the file writting is correct. Checked with a hex editor and should be correct.
So my guesses are that my fault is at the reading of the file.
Forgot to mention that a restriction of the project is that system calls for I/O are mandatory.
Any help would be very much appreciated.
Thanks in advance.
Edit1:
Changed *my_stack_read() as @AndrewHenle suggested, the output is still not the expected.
struct my_stack *my_stack_read(char *filename) {
int fileDesc = open(filename, O_RDONLY, S_IRUSR);
if(fileDesc == -1) {
return NULL; // Error open();
}
char *buffer = malloc(sizeof(int));
ssize_t readBytes;
readBytes = read(fileDesc, buffer, sizeof(int));
if(readBytes == -1) {
return NULL;
}
int dataSize = 0;
dataSize = (int) *buffer; // parse data Size from buffer.
struct my_stack *stack;
stack = malloc(sizeof(struct my_stack));
stack = my_stack_init(dataSize); // initialize Stack
buffer = realloc(buffer, stack -> size);
if(buffer == NULL){
return NULL;
}
else{
while(read(fileDesc, buffer, stack -> size) > 0) {
int push = my_stack_push(stack,buffer);
if(push == -1){
printf("Error en my_stack_read: Push error.\n");
return NULL;
}
}
close(fileDesc);
return stack;
}
Solution:
I found my error in *my_stack_read:
while(read(fileDesc, buffer, stack -> size) > 0) {
int push = my_stack_push(stack,buffer);
if(push == -1){
printf("Error en my_stack_read: Push error.\n");
return NULL;
}
buffer = malloc(stack -> size);
}
buffer = malloc(stack -> size); I had allocated the memory outside the for loop, and I didn't allocate for the subsequent reads.
I thought the read would use same direction overwritting it's content but it seems this is not possible.
Could anyone explain the reason?
Thank you all.