My answer is simple: However you want.

More specifically, scanf cannot seek line 5. (neither can fseek -- they count bytes, not lines.) To get to line 5, read 4 lines:

Code:

int line=5;
char buf[512];
FILE *fp=fopen("file.txt", "r");
while(--line) fgets(buf, 512, fp);
// You are now at line 5.
code_to_read_fifth_line();

Next, rule #1 of C is "never, ever, ever use fscanf". If you absolutely must use scanf, use sscanf. read one line at a time with fgets like I showed you, clean them up with chomp like I showed you, then call sscanf(string, "whatever", arguments);. That will avoid most of scanf's inevitable stumbling blocks.

First problem, scanf has a buffering issue, which is probably why it's not doing what you expect. The first time you call it, it will read until a newline is detected. The second time you call it, it reads until the exact same newline is detected! That newline was never matched, so is still there.

However, fscanf has another problem. What if one of those lines is 1000 bytes but your buffer is only 10? Crash!

You can fix the first issue, to a point. You have to tell fscanf everything it should expect, including the stuff you don't want to keep. Only % codes get read into variables, other stuff gets silently skipped. fscanf(fp, "%[^\r\n]\r\n", c); But if you ever end up with input you didn't specify, fscanf will quite literally choke on it. That's why I specify \r\n here instead of \n. That was a crash issue in software I ported from Windows to UNIX - fscanf had to be amended to accommodate Windows-style carriage returns. \r\n works with both here.

A better example of the way scanf thinks might be sscanf("abcde12345fghijk", "abcde%dfghijk", &number); abcde and fghijk get matched without being stored, only %d is stored because of the %. If you fed it the string "abcdf12345fghijk" it would read "abcd" and stop at f, where it stops agreeing with the string you gave it. The & is required for atomic types - integers and floating point. Strings don't get the & because character arrays are already pointers as far as C's concerned.

Then what do you want? Your questions are both too specific and not specific enough because you're making hasty choices looking for solutions to problems we don't know about. Like the "inserting text into header file" question as a workaround to actually loading a normal text file. Please explain and I might be able to do what you want. How is telnet involved here? What are you actually doing?