How to parse this data of unknown size - c++

Question

I have a simple text file containing instructions per a line. e.g
A 1 1
B 2 1 A
C 3 1 A
D 4 1 B C
Basic syntax is Letter, Num, Num, Letter(s)
I just don't know what function I should be calling to parse the data, and how to parse it in the given syntax. I feel like there's so many ways to do it.

Answer 1

The following C++ example shows one of possible way to read single characters from file, controlling end of line:
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
using namespace std;
int main(void)
{
ifstream inpFile("test.txt");
string str;
char c;
while (inpFile.good()) {
// read line from file
getline(inpFile, str);
// make string stream for reading small pieces of data
istringstream is(str);
// read data ingnoring spaces
do
{
is >> c; // read a single character
if (!is.eof()) // after successful reading
cout << c << " "; // output this character
} while (is.good()); // control the stream state
cout << "[End of line]" << endl;
}
cout << "[End of file]" << endl;
}
Here istringstream is used to process single line that is got by getline.
After reading a char with is >> c value in c can be checked for content, e.g.:
if (!is.eof()) // after successful reading
{
// analyze the content
if ( isdigit(c) )
cout << (c - '0') << "(number) "; // output as a digit
else
cout << c << "(char) "; // output as a non-number
}
Note: if file can contain not single characters / digits, but numbers and words, type of c should be appropriate (e.g. string)

Answer 2

In C++, read an entire line and make a stream from it, then read from that stream with >>.
Example:
std::ifstream file(filename);
std::string line;
while (file.getline(line))
{
std::istringstream in(line);
char letter;
int number1;
int number2;
std::vector<char> letters;
if (in >> letter >> number1 >> number2)
{
char letter2;
while (in >> letter2)
{
letters.push_back(letter2);
}
}
}

Answer 3

This is C example that read lines, and then goes (using pointer) from the beginning to output readable characters (with code greater than 32):
#include <stdio.h>
#include <ctype.h>
#define MAX_LINE_LEN 80
int main(void)
{
FILE * inpFile = fopen("test.txt", "r");
char buf[MAX_LINE_LEN];
char *p;
while (!feof(inpFile))
{
// read a line from file
if (fgets(buf, MAX_LINE_LEN, inpFile) != NULL)
{
p = buf; // start from the beginning of line
// reading data from string till the end
while (*p != '\n' && *p != '\0')
{
// skip spaces
while (isspace(*p) && *p != '\n') p++;
if (*p > 32)
{
// output character
printf("%c ", *p);
// move to next
p++;
}
}
}
printf("[End of line]\n");
}
printf("[End of file]\n");
return 0;
}
To extract numbers and words from the line you can do something like:
// reading data from string till the end
while (*p != '\n' && *p != '\0')
{
// skip spaces
while (isspace(*p) && *p != '\n') p++;
if (*p > 32)
{
int num;
char word[MAX_LINE_LEN];
// trying to read number
if (sscanf(p, "%i", &num))
{
printf("%i(number) ", num);
}
else // read string
{
sscanf(p, "%s", word);
printf("%s(string) ", word);
}
// move to next space in the simplest way
while (*p > 32) p++;
}
}