Navigating through a file lines - C - c

Question

Is there any way to navigate through a file with the option of moving up and down the line number instead of sequentially?
As of now, my code uses fgets to get the last line of ascii characters within the file, but through my research, I haven't found a smarter way of iterating through the file.
For example:
file.txt contains:
"hello\n"
"what's up?\n"
"bye"
I need to be able to return "bye" at first, but then using key presses, print "what's up\n", and go back down to "bye" through another key press.

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
FILE *infile;
char *infile_contents;
unsigned int infile_size;
// to read all of the file
infile = fopen("file.txt", "rb");
fseek(infile, 0, SEEK_END);
infile_size = ftell(infile);
fseek(infile, 0,SEEK_SET);
infile_contents = malloc(infile_size+1);
fread(infile_contents, infile_size, 1, infile);
fclose(infile);
infile_contents[infile_size]=0;
// to store the beginning of lines and replace '\n' with '\0'
size_t num_lines = 1, current_line = 1, length;
char **lines = malloc(sizeof(char*)), **lines1, *tmp;
lines[0] = infile_contents;
while(tmp = strchr(infile_contents, '\n'))
{
// to resize lines if it is not big enough
if(num_lines == current_line)
{
lines1 = lines;
lines = malloc((num_lines<<1)*sizeof(char*));
memcpy(lines, lines1, num_lines*sizeof(char*));
memset(lines+num_lines, 0, num_lines*sizeof(char*));
num_lines <<= 1;
free(lines1);
}
*tmp=0;
infile_contents = tmp+1;
lines[current_line++] = infile_contents;
}
// to print the lines
num_lines = current_line-1;
current_line = num_lines;
// to skip the last line if it is empty
if(!lines[current_line][0])
{
num_lines--;
current_line = num_lines;
}
while(1)
{
printf("%s",lines[current_line]);
if(getchar())// change to the condition for going down
{
if(current_line)
current_line--;
else
current_line=num_lines;
}
else
{
if(current_line==num_lines)
current_line=0;
else
current_line++;
}
}
}