Read lines from an input file of varying line sizes-CodePudding

Currently, I am using getline to read lines from a file and I can access individual characters the following way from stdin:

char buffer[1024];
while((lineSize = getline(&line, &len, stdin)) != -1) {
            if (line[0] != 84) {
                // ...
                continue; // continue to next line in file
            }
            if (line[0] == 84){ // (the 'T' character)
                printf("TEST: Line Value: %s\n", line);
                buffer[0] = line[1]; // this is a single digit number in char form
                buffer[1] = '\0';
                // send buffer somewhere
                send(clientSocket, buffer, strlen(buffer), 0);
                // ...
}

A sample file is as follows:

T3
T9
S0
S4
T55
T6

However, as you can see, I run into issues when a number > 9 is given such as the T55 line here. I can only grab the first digit with this method. Therefore, I may have to completely redo the way I read a file. Is there a better and simple way I can read through an input file and check the first character and make the remaining character(s) into an int until the end of a line? (Max the integer can be is 100 btw)

CodePudding user response：

Continuing from my comments, you can use fgets() to read line and then use sscanf() with the format string of " %c%d%n" to extract the first character and converting the next set of digits to an int and finally obtaining to total number of characters consumed by sscanf() in that conversion using the "%n" specifier. You validate that both the character and integer conversion took place and that the first non-whitespace character read was 'T'. You can then use mychar and myint as desired and use mylen as the length to use with send.

(note: you can scan forward in line to determine if any whitespace was included at the beginning and ignore than in your call to send() -- that is left to you)

Putting it altogether, you can so something like:

  char line[1024],
       mychar = 0;
  int myint = 0,
      mylen;
  
  /* read using fgets */
  while (fgets (line, sizeof line, stdin)) {
    /* parse with sscanf, validate both conversions and 'T' as 1st char,
     * use "%n" to get number of chars through int conversion
     */
    if (sscanf (line, " %c%d%n", &mychar, &myint, &mylen) != 2 || 
                mychar != 'T') {
      fputs ("error: invalid format.\n", stderr);
      continue;
    }
    
    send (clientSocket, line, mylen, 0);    /* send mylen chars */
  }

To be more specific, I will need to see your Minimal Complete Reproducible Example to ensure there is nothing outside what you have posted that will impact the code above.

Adding Example

Adding a short example to show the result of parsing under expected and unexpected input with the above, and adding the scanning forward to remove leading whitespace in the line, a short program that reads input from stdin and writes to stdout, outputting the lines matching 'T'(int), you could do:

#include <stdio.h>
#include <unistd.h>
#include <ctype.h>

int main (void) {

  char line[1024],
       mychar = 0,
       nl = '\n';
  int myint = 0,
      mylen;
  
  /* read using fgets */
  while (fgets (line, sizeof line, stdin)) {
    char *p = line;
    /* parse with sscanf, validate both conversions and 'T' as 1st char,
     * use "%n" to get number of chars through int conversion
     */
    if (sscanf (line, " %c%d%n", &mychar, &myint, &mylen) != 2 || 
        mychar != 'T') {
      fprintf (stderr, "error: invalid format: %s", line);
      continue;
    }
    
    while (isspace (*p)) {    /* reamove leading whitespace */
      p  = 1;
      mylen -= 1;
    }
    
    // send (clientSocket, p, mylen, 0);    /* send mylen chars */
    write (STDOUT_FILENO, p, mylen);
    write (STDOUT_FILENO, &nl, 1);
  }
}

(note: write (STDOUT_FILENO, &nl, 1); is simply included above to output a newline after each output -- it would not be part of what you send() over your socket -- unless the receiving program is using the '\n' as the line termination character)

Example Input File:

$ cat dat/charint.txt
T4
T44
T444
 TT
 T3 and more gibberish
P55

(note: leading whitespace and trailing characters included in last two lines beginning with 'T', including the invalid line format " TT")

Example Use/Output

$ ./bin/charandintsend < dat/charint.txt
T4
T44
T444
error: invalid format:  TT
T3
error: invalid format: P55

Let me know if you have questions, or if I misunderstood some aspect of your question.