C struct value resetting to NULL - c

Question

I'm working on a school project where I have to store PPM data into structs. I have an issue with an array of strings inside the struct.
typedef struct {
char **comments;
} PPM;
I have 3 functions that uses this struct.
PPM *getPPM() is used to get all the PPM data from file and store it into the struct
void showPPM(PPM * img) to show the image data in terminal
PPM *encode(PPM *img) which is used to change the LSB of the RGB values of the image
The problem is that getPPM works as intended and gets all the comments into the comments array in getPPM. It displays them fine if I do it like this:
PPM *p = getPPM(fin);
showPPM(p);
But if I try to call it with the encode function like this:
PPM *p = getPPM(fin);
PPM *g = encode(p);
showPPM(g);
the debugger shows that as soon as the program enters the encode function, the comments value resets to NULL even though this function doesn't even touch comments. Is the way I am calling these functions wrong or is there something wrong with my code? I will try to provide the minimal code if the problem is not the way the functions are being called, as the code is big and everything is dependent on one another.
I'm very new to C language. I tried understanding the problem for hours but can't find a solution anywhere. Any help would be greatly appreciated.
EDIT: This is as small as I could make it.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//Structures
typedef struct {
int r, g, b;
} pixels;
typedef struct {
char format[3];
char **comments;
int width, height, maxColors, commentCounter;
pixels **pixelValues;
} PPM;
// Functions declarations
PPM *getPPM(FILE * f);
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret);
void showPPM(PPM * im);
static int *decimalToBinary(const char *message, unsigned int length);
// Main method
int main(int argc, char **argv) {
FILE * fin = fopen(argv[1], "r");
if(fin == NULL) {
perror("Cannot open file");
exit(1);
}
PPM *p = getPPM(fin);
PPM *g = encode(p, "test", 5, 1);
showPPM(g);
return 0;
}
/*
* This function is used to get the image data from a file and populate
* our strutures with it.
*/
PPM *getPPM(FILE * f) {
// Allocate the memory for structure and check if it was successful
PPM *pic = (PPM *) malloc(sizeof(PPM));
if(!pic) {
perror("Unable to allocate memory for structure");
exit(1);
}
char line[100]; // Expecting no more than 100 characters per line.
pic->commentCounter = 0; // This is the counter to keep size if there are more than one comments
int pixelsCounter = 0; // Counter for pixels' array
pic->comments = malloc(sizeof(char *));
pic->pixelValues = malloc(sizeof(PPM));
int lineCounter = 0;
if((pic->comments) == NULL) {
perror("Unable to allocate memory for pixels");
exit(1);
}
while(fgets(line, sizeof(line), f)) {
// Reference: https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input
size_t length = strlen(line);
if(length > 0 && line[length-1] == '\n') {
line[--length] = '\0';
}
// Assigning the file format
if(line[0] == 'P') {
pic->format[0] = line[0];
pic->format[1] = line[1];
pic->format[2] = '\0';
}
//Populate comments into struct PPM
if(line[0] == '#') {
// Reallocate/allocate the array size each time a new line of comment is found
if(pic->commentCounter != 0) {
pic->comments = realloc(pic->comments, (pic->commentCounter+1) * sizeof(char *));
}
// Allocate the memory for the string
pic->comments[pic->commentCounter] = malloc(100 * sizeof(char));
// Write the at commentCounter position of the array; character by character
int i = 0;
while(line[i] != '\0') {
pic->comments[pic->commentCounter][i] = line[i];
i++;
}
pic->comments[pic->commentCounter][i] = '\0';
pic->commentCounter++;
}
/*
* Loading the max color property of the file which is gonna be 3 letters (Usually 255)
* and checking if we previously got maxColors in our construct or not. If we didn't
* then we load this value into the consturct and the condition will never validate
* throughout the iterations
*/
if(strlen(line) == 3 && pic->maxColors == 0 && line[0] != '#') {
pic->maxColors = atoi(line);
continue;
}
/*
* Check if the length of string > 3, which means it is going to be a
* number, potentially RGB value or a comment. But since width & height
* comes before RGB values, our condition will fail once we have found
* the width/height for the next iteration. That's why this condition
* only checks if it is a comment or a numbered value of length > 3
*/
if((strlen(line) > 3) && (pic->width == 0) && (line[0] != '#')) {
char *width = strtok(line, " ");
char *height = strtok(NULL, " ");
pic->width = atoi(width);
pic->height = atoi(height);
continue;
}
/*
* If the width/height and maxColors have been found, that means every
* other line is either going to be the RGB values or a comment.
*/
if((pic->width != 0) && (pic->maxColors != 0) && (line[0] != '#')) {
// length(line) > 3 means all the RGB values are in same line
if(strlen(line) > 3) {
char *val1 = strtok(line, " ");
char *val2 = strtok(NULL, " ");
char *val3 = strtok(NULL, " ");
// pixelsCounter = 0 means it's the first element.
if(pixelsCounter != 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(val1);
pic->pixelValues[pixelsCounter]->g = atoi(val2);
pic->pixelValues[pixelsCounter]->b = atoi(val3);
pixelsCounter++;
} else if(strlen(line) <= 3) {
/*
* If each individual RGB values are in a separete lines, we will
* use a switch case and a line counter to keep track of where the
* values were inserted and when to know when we got RGB values for
* one pixel
*/
if(pixelsCounter != 0 && lineCounter == 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
switch(lineCounter) {
case 0 :
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(line);
lineCounter++;
continue;
case 1 :
pic->pixelValues[pixelsCounter]->g = atoi(line);
lineCounter++;
continue;
case 2 :
pic->pixelValues[pixelsCounter]->b = atoi(line);
lineCounter=0;
pixelsCounter++;
continue;
default:
continue;
}
}
}
}
pic->pixelValues[pixelsCounter] = NULL;
fclose(f);
return pic;
}
void showPPM(PPM * im) {
printf("%s\n",im->format);
int k = 0;
while(k < im->commentCounter) {
printf("%s\n", im->comments[k]);
k++;
}
printf("%d %d\n", im->width, im->height);
printf("%d\n",im->maxColors);
int j = 0;
while(im->pixelValues[j] != NULL) {
printf("%d %d %d\n", im->pixelValues[j]->r, im->pixelValues[j]->g, im->pixelValues[j]->b);
j++;
}
}
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret) {
int *binaryMessage = decimalToBinary(message, mSize);
int i, j = 0, lineCounter = 0;
for(i = 0; i < 40; i++) {
switch(lineCounter) {
case 0 :
im->pixelValues[j]->r |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 1 :
im->pixelValues[j]->g |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 2 :
im->pixelValues[j]->b |= binaryMessage[i] << 0;
lineCounter=0;
j++;
continue;
default:
continue;
}
}
return im;
}
/*
* Converts a string into binary to be used in encode function. It
* first converts each letter of the string into ascii code. Then
* finds and stores each of the 8 bits of that int (ascii code of
* the letter) sequentially in an array.
*/
static int *decimalToBinary(const char *message, unsigned int length) {
/*
* malloc is used here instead of [] notation to allocate memory,
* because defining the variable with [] will make its scope
* limited to this function only. Since we want to access this
* array later on, we use malloc to assign space in the memory
* for it so we can access it using a pointer later on.
*/
int k=0, i, j;
unsigned int c;
unsigned int *binary = malloc(8 * length);
for(i = 0; i < length; i++) {
c = message[i];
for(j = 7; j >= 0; j--,k++) {
/*
* We check here if the jth bit of the number is 1 or 0
* using the bit operator &. If it is 1, it will return
* 1 because 1 & 1 will be true. Otherwise 0.
*/
if((c >> j) & 1)
binary[k] = 1;
else
binary[k] = 0;
}
}
return binary;
}
PPM file:
P3
# CREATOR: GIMP PNM Filter Version 1.1
# Amazing comment 2
# Yet another amazing comment
400 530
255
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0

Answer 1

in decimalToBinar
unsigned int *binary = malloc(8 * length);
must be
unsigned int *binary = malloc(8 * length * sizeof(int));
new code is :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
//Structures
typedef struct {
int r, g, b;
} pixels;
typedef struct {
char format[3];
char **comments;
int width, height, maxColors, commentCounter;
pixels **pixelValues;
} PPM;
// Functions declarations
PPM *getPPM(FILE * f);
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret);
void showPPM(PPM * im);
static int *decimalToBinary(const char *message, unsigned int length);
// Main method
int main(int argc, char **argv) {
FILE * fin = fopen(argv[1], "r");
if(fin == NULL) {
perror("Cannot open file");
exit(1);
}
PPM *p = getPPM(fin);
PPM *g = encode(p, "test", 5, 1);
showPPM(g);
free(p->comments);
free(p);
return 0;
}
/*
* This function is used to get the image data from a file and populate
* our strutures with it.
*/
PPM *getPPM(FILE * f) {
// Allocate the memory for structure and check if it was successful
PPM *pic = (PPM *) malloc(sizeof(PPM));
if(!pic) {
perror("Unable to allocate memory for structure");
exit(1);
}
char line[100]; // Expecting no more than 100 characters per line.
pic->commentCounter = 0; // This is the counter to keep size if there are more than one comments
int pixelsCounter = 0; // Counter for pixels' array
pic->comments = malloc(sizeof(char *));
pic->pixelValues = malloc(sizeof(PPM));
int lineCounter = 0;
if((pic->comments) == NULL) {
perror("Unable to allocate memory for pixels");
exit(1);
}
pic->width = 0;
pic->height = 0;
pic->maxColors = 0;
while(fgets(line, sizeof(line), f)) {
// Reference: https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input
size_t length = strlen(line);
if(length > 0 && line[length-1] == '\n') {
line[--length] = '\0';
}
// Assigning the file format
if(line[0] == 'P') {
pic->format[0] = line[0];
pic->format[1] = line[1];
pic->format[2] = '\0';
}
//Populate comments into struct PPM
if(line[0] == '#') {
// Reallocate/allocate the array size each time a new line of comment is found
if(pic->commentCounter != 0) {
pic->comments = realloc(pic->comments, (pic->commentCounter+1) * sizeof(char *));
}
// Allocate the memory for the string
pic->comments[pic->commentCounter] = malloc(100 * sizeof(char));
// Write the at commentCounter position of the array; character by character
int i = 0;
while(line[i] != '\0') {
pic->comments[pic->commentCounter][i] = line[i];
i++;
}
pic->comments[pic->commentCounter][i] = '\0';
pic->commentCounter++;
}
/*
* Loading the max color property of the file which is gonna be 3 letters (Usually 255)
* and checking if we previously got maxColors in our construct or not. If we didn't
* then we load this value into the consturct and the condition will never validate
* throughout the iterations
*/
if(strlen(line) == 3 && pic->maxColors == 0 && line[0] != '#') {
pic->maxColors = atoi(line);
continue;
}
/*
* Check if the length of string > 3, which means it is going to be a
* number, potentially RGB value or a comment. But since width & height
* comes before RGB values, our condition will fail once we have found
* the width/height for the next iteration. That's why this condition
* only checks if it is a comment or a numbered value of length > 3
*/
if((strlen(line) > 3) && (pic->width == 0) && (line[0] != '#')) {
char *width = strtok(line, " ");
char *height = strtok(NULL, " ");
pic->width = atoi(width);
pic->height = atoi(height);
continue;
}
/*
* If the width/height and maxColors have been found, that means every
* other line is either going to be the RGB values or a comment.
*/
if((pic->width != 0) && (pic->maxColors != 0) && (line[0] != '#')) {
// length(line) > 3 means all the RGB values are in same line
if(strlen(line) > 3) {
char *val1 = strtok(line, " ");
char *val2 = strtok(NULL, " ");
char *val3 = strtok(NULL, " ");
// pixelsCounter = 0 means it's the first element.
if(pixelsCounter != 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(val1);
pic->pixelValues[pixelsCounter]->g = atoi(val2);
pic->pixelValues[pixelsCounter]->b = atoi(val3);
pixelsCounter++;
} else if(strlen(line) <= 3) {
/*
* If each individual RGB values are in a separete lines, we will
* use a switch case and a line counter to keep track of where the
* values were inserted and when to know when we got RGB values for
* one pixel
*/
if(pixelsCounter != 0 && lineCounter == 0) {
// Reallocate memory each time a new R G B value line is found
pic->pixelValues = realloc(pic->pixelValues, (pixelsCounter + 1) * sizeof(PPM));
}
switch(lineCounter) {
case 0 :
pic->pixelValues[pixelsCounter] = malloc(12 * sizeof(pixels));
pic->pixelValues[pixelsCounter]->r = atoi(line);
lineCounter++;
continue;
case 1 :
pic->pixelValues[pixelsCounter]->g = atoi(line);
lineCounter++;
continue;
case 2 :
pic->pixelValues[pixelsCounter]->b = atoi(line);
lineCounter=0;
pixelsCounter++;
continue;
default:
continue;
}
}
}
}
pic->pixelValues[pixelsCounter] = NULL;
fclose(f);
return pic;
}
void showPPM(PPM * im) {
printf("%s\n",im->format);
int k = 0;
while(k < im->commentCounter) {
printf("%s\n", im->comments[k]);
k++;
}
printf("%d %d\n", im->width, im->height);
printf("%d\n",im->maxColors);
int j = 0;
while(im->pixelValues[j] != NULL) {
printf("%d %d %d\n", im->pixelValues[j]->r, im->pixelValues[j]->g, im->pixelValues[j]->b);
j++;
}
}
PPM *encode(PPM *im, char *message, unsigned int mSize, unsigned int secret) {
int *binaryMessage = decimalToBinary(message, mSize);
int i, j = 0, lineCounter = 0;
for(i = 0; i < 40; i++) {
switch(lineCounter) {
case 0 :
im->pixelValues[j]->r |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 1 :
im->pixelValues[j]->g |= binaryMessage[i] << 0;
lineCounter++;
continue;
case 2 :
im->pixelValues[j]->b |= binaryMessage[i] << 0;
lineCounter=0;
j++;
continue;
default:
continue;
}
}
free(binaryMessage);
return im;
}
/*
* Converts a string into binary to be used in encode function. It
* first converts each letter of the string into ascii code. Then
* finds and stores each of the 8 bits of that int (ascii code of
* the letter) sequentially in an array.
*/
static int *decimalToBinary(const char *message, unsigned int length) {
/*
* malloc is used here instead of [] notation to allocate memory,
* because defining the variable with [] will make its scope
* limited to this function only. Since we want to access this
* array later on, we use malloc to assign space in the memory
* for it so we can access it using a pointer later on.
*/
int k = 0, i, j;
unsigned int c;
unsigned int *binary = malloc(8 * length * sizeof(int));
for(i = 0; i < length; i++) {
c = message[i];
for(j = 7; j >= 0; j--,k++) {
/*
* We check here if the jth bit of the number is 1 or 0
* using the bit operator &. If it is 1, it will return
* 1 because 1 & 1 will be true. Otherwise 0.
*/
if((c >> j) & 1)
binary[k] = 1;
else
binary[k] = 0;
}
}
return binary;
}