Segmentation fault on loader for Sokoban game in C - c

Question

So I'm trying to write a code in C that would create an array of characters from a file looking like :
10 8
##########
###### ##
# $ $ ##
# # .# ##
# . #.# #
##$# * #
## #####
##########
But I'm stuck with a segmentation fault and I've been searching where it could come from unsuccessfully... I would really appreciate if someone could read my code and give me his/her feedback...
Thanks in advance !
//We define a structure representing a map (for the Sokoban game)
typedef struct map map;
struct map{
int width;
int height;
int x;
int y;// x and y are the position of the player
char* p_char; //p_char is pointing an array which will contain the elements of the map, the characters currently on the file above
};
//The function that reads the file and store the characters in an array
char* ReadMap(const char const* filename)
{
FILE* p_file = fopen(filename, "r");
char* p_array = NULL;
if (p_file = NULL) {
exit(EXIT_FAILURE);
}
else{
size_t size=1;
while (getc(p_file)!=EOF) {
size++;
}
p_array=(char*)malloc(sizeof(char)*size);
fseek(p_file,0,SEEK_SET);
for(size_t i=3; i<size-1; i++) {
p_array[i]=(char)getc(p_file);//i=3 cause we don't want the 2 first int, representing the size of the array
}
p_array[size-1]='\0';
fclose(p_file);
}
return p_array;
}
int main(int argc, char *argv[]){
if (argc != 2) {
fprintf(stderr, "You must provide a file name!\n");
exit(EXIT_FAILURE);
}
//We define a map structure
map map_loaded;
FILE *p_file1 = NULL;
p_file1=fopen(argv[1],"r");
if (p_file1==NULL) {
fprintf(stderr, "Cannot read file %s!\n", argv[1]);
exit(EXIT_FAILURE);
}
//we're trying to recover width and height, two int at the beginnning of the file
int width=0;
map_loaded.width=width;
int height=0;
map_loaded.height=height;
int fscanf_result=0;
fscanf_result=fscanf(p_file1, "%d %d\n", &width, &height);
char* p_char=NULL;
map_loaded.p_char=p_char;
p_char=ReadMap(argv[1]);
if (p_char != NULL) {
printf("%s\n", p_char);
free(p_char);
}
}

Answer 1

The cause of Segmentation Fault is the expression p_file = NULL used as condition.
p_file = NULL is an assignment expression. It sets p_file to NULL and evaluated to the assigned value, which is NULL.
NULL is treated as false when used as condition.
On the other hand, condition being false indicates file open success when the condition is a comparison p_file == NULL.
In this case, the condition becomes false when p_file is not NULL.
For that reason, code that expects that p_file is not NULL is written
in the else clause.
The code includes statements that pass p_file to fgetc().
As a result, NULL is passed to fgetc() and this is one possible reason of Segmentation Fault.
Note that your code still seems wrong after getting rid of this Segmentation Fault.
In the example, the size part is 10 8, which is 4-character long. This implies skipping "3 characters" doesn't make sense.
Also note that starting i from 3 won't skip file contents and just leave first 3 elements of the array uninitialized as Some programmer dude points.
Instead of that, you can "skip the first line". In other words, you can "skip until the first newline character".
size_t size=1;
int c;
while (getc(p_file)!=EOF) {
size++;
}
fseek(p_file,0,SEEK_SET);
while ((c=getc(p_file))!='\n' && c!=EOF) { // drop the first line
size--;
}
p_array=(char*)malloc(sizeof(char)*size);
if (p_array!=NULL) { // for in case malloc() fails
for(size_t i=0; i<size-1; i++) {
p_array[i]=(char)getc(p_file);
}
p_array[size-1]='\0';
}
fclose(p_file);
One way to enable width*i+j indexing is removing newline characters by adding this code after the line p_array[i]=(char)getc(p_file);:
if (p_array[i] == '\n') { // if the character is newline, remove it
i--; // rollback
size--; // adjust size for the newline character dropped
}