how to make fscanf, scan a single word instead of whole line

Question

There is a text file called 1.txt like below that contains certain names, I want to add them to a linked list however the code doesn't scan only one name but the whole line, how can I make fscanf so that it only scans a single name?

Example 1.txt:

ana,bob,max,dolores

My code:

FILE *fp = fopen("1.txt", "rt");
while (!feof(fp)) {
    char name_in[100];
    fscanf(fp, "%s,", name_in);
    printf("%s", name_in);
    addnewnode(head, name_in);
}
fclose(fp);

something like [this](http://stackoverflow.com/questions/12911299/read-csv-file-in-c) ? — Zorgatone, Jan 13 '17 at 11:39
Possible duplicate of [In C, how should I read a text file and print all strings](http://stackoverflow.com/questions/3463426/in-c-how-should-i-read-a-text-file-and-print-all-strings) — kiner_shah, Jan 13 '17 at 13:13

score 2 · Answer 1 · edited May 23 '17 at 11:52

2

The problem is that with the "%s" format, then scanf will not stop scanning until it hit the end of the input or a whitespace. That means you can't use scanf alone to parse your input.

Instead I suggest you read your whole line into a buffer, for example using fgets. Once you have it then you can use strtok in a loop to tokenize the line.

Not using scanf also sidesteps a big problem with your format string: Namely that it will look for a trailing comma in the input. If there's no comma at the end of the line (like in your example) then scanf will just block. It will block until there is a comma, but if you don't give it a comma then it might block forever. Either that or you will not get the last entry because scanf will fail. Checking what scanf returns is crucial.

Also, I strongly suggest you read Why is “while ( !feof (file) )” always wrong?.

edited May 23 '17 at 11:52

Community

1
1

answered Jan 13 '17 at 11:36

Some programmer dude

400,186
35
402
621

but i did put a comma (,) before the %s doesn't that count for something? – ATheCoder Jan 13 '17 at 11:38
@ArashArbabi that just means a string followed by a comma, but a string can contain a comma, so it's ignored – Zorgatone Jan 13 '17 at 11:40
@ArashArbabi No, the `"%s"` format is *greedy* and will read until it hits a space or the end of the input. *Then* it will attempt to match your trailing comma. – Some programmer dude Jan 13 '17 at 11:40
is there anyway that I could do this without using strtok? – ATheCoder Jan 13 '17 at 11:47
1

@ArashArbabi Of course there is. For example by reading one character at a time, append them into a buffer, and use the (*terminated*) buffer when you hit a comma, end of line or end of file. – Some programmer dude Jan 13 '17 at 11:56

chux - Reinstate Monica · Answer 2 · 2017-01-13T16:29:25.377

What's in a name?

A name is usually thought of as containing letters, maybe spaces and some other characters. Code needs to be told what char make up a name, what are valid delimiters and handle other unexpected char.

"%s" only distinguishes between white-space and non-white-space. It treats , the same as letters.

"%width[A-Za-z' ]" will define a scanset accepting letters, ' and space. It will read/save up to width characters before appending a null character.

Always a good idea to check the return value of a input function before using the populated objects.

FILE *fp = fopen("1.txt", "rt");
if (fp == NULL) Handle_Error();

// end-of-file signal is not raised until after a read attempt.
// while (!feof(fp)) {

char name_in[100];
char delimiter[2];
int count;
while ((count = fscanf(fp, "%99[A-Za-z' ]%1[,\n]", name_in, delimiter)) == 2) {
  printf("<%s>%s", name_in, delimiter);
  addnewnode(head, name_in);
  if (delimiter[0] == '\n') {
    ; // Maybe do something special at end-of-line
  }
}
fclose(fp);

// Loop stopped unexpectedly
if (count != EOF || !feof(fp)) {
  puts("Oops");
}

More robust code would read the line like with fgets() and then process the string. Could use similar code as above but with sscanf()

To include - in a scanset so code can handle hyphenated names, list it first. You may want to allow other characters too.

"%width[-A-Za-z' .]"

how to make fscanf, scan a single word instead of whole line

2 Answers2