Server Implementation in C - html

Question

I'm currently working on a server which is part of my course requirement. The specs require me to parse a request line and store the appropriate data as absolute path (abs_path) and query.
Here is my code:
bool parse(const char* line, char* abs_path, char* query)
{
int space = 0;
if (strchr(line, '"') != NULL)
{
error(400);
return false;
}
for (int i = 0; line[i] != '\0'; i++)
{
if (line[i] == ' ')
{
space++;
}
}
if (space != 2)
{
error(400);
return false;
}
if (strncmp("GET ", line, 4) != 0)
{
error(405);
return false;
}
line = strchr(line, ' ');
line++;
if (strncmp("/", line, 1) != 0)
{
error(501);
return false;
}
int j = 0;
int k = 4;
while (line[k] != ' ')
{
int m = k;
abs_path[j] = line[k];
j++;
if (line[k+1] == '?')
{
abs_path[j] = '\0';
int l = 0;
m = k+2;
while (line[m] != ' ')
{
query[l] = line[m];
l++;
m++;
}
if (line[m] == ' ' && l == 0)
{
query[0] = '\0';
}
}
k = m;
k++;
if (line[k] == ' ')
{
abs_path[j] = '\0';
break;
}
}
char* last = strrchr(line, ' ');
last++;
if (strcmp("HTTP/1.1", last) != 0)
{
error(505);
return false;
}
free(abs_path);
return true;
}
I keep getting a segmentation fault with this. After some debugging, I've found the segmentation fault to be eliminated if I declare, on line 20, abs_path as an array instead of a pointer. However, it is necessary for me to declare abs_path as a pointer, so I need another solution to this. Can someone explain to me what exactly I am doing wrong with regards to strings and their handling?
I have been quite rusty with this due to personal reasons so pardon me if I misunderstand something basic.
Thank you in advance!

Answer 1

You need to allocate memory for the char*. An array does this automatically during compile time. Try malloc.
char* abs_path = 0;
abs_path = (char*)malloc(256);
Essentially, malloc performs an operating system call to reserve sequential memory from the heap. The argument of malloc is how many bytes to reserve. Therefore, you should be aware that the example above enables the abs_path char* to point to a string that is at max 255 characters (leaving 1 byte for the null character '\0'). Don't let your code write more than 255 characters or you will overwrite other data in memory, which is why you received a seg-fault before.
As someone else noted, you should DEFINITELY free up memory reserved dynamically with malloc.
free(abs_path);