LineReader

The class LineReader is an abstract base class for line-reading classes. There are two implementations, LineReader_std and LineReader_gz.

LineReader_std lets you comfortably read lines from a text file, whereas you can read lines directly from a gzipped text file. There are tw implementations

Code:
LineReader.h
LineReader.cpp

Public Methods

createInstance

(LineReader_std and LineReader_gz)

static LineReader *createInstance(const std::string sFileName, const std::string sMode, int iLineLen=MAX_LINE2);

Create a LineReader for the specified file.

sFileName

Name of the file to be read.

sMode

File access mode, usually “rt”.

iLineLen

Size of internal line buffer.

Returns a LineReader_xxx object on success, or NULL on failure.

createInstance

(LineReader_std only)

static LineReader *createInstance(FILE *fIn, int iLineLen=MAX_LINE2);

Create a LineReader for the opened file.

fIn

File handle to an opened text file.

iLineLen

Size of internal line buffer.

Returns a LineReader_std object on success, or NULL on failure.

constructor

LineReader_std(const std::string sFileName, const std::string sMode, int iLineLen=MAX_LINE2);
LineReader_gz(const std::string  sFileName, const char *pMode, int iLineLen=MAX_LINE2);

The constructor.

sFileName

Name of the file to be read.

sMode

File access mode, usually “rt”.

iLineLen

Size of internal line buffer.

constructor

LineReader_std(FILE *fIn, int iLineLen=MAX_LINE2);
LineReader_gz(gzFile fIn, int iLineLen=MAX_LINE2);

Construcor for opened file.

fIn

File handle to an opened text file.

iLineLen

Size of internal line buffer

destructor

~LineReader_std();
~LineReader_gz();

The destructor.

getNextLine

virtual char *getNextLine(int iMode=GNL_IGNORE_ALL);

Get the next line.

iMode

Accesss mode:

GNL_IGNORE_NONE

0

pass every line

GNL_IGNORE_BLANKS

1

drop blank lines

GNL_IGNORE_COMMENTS

2

drop #-comment lines

GNL_IGNORE_MATCOMM

4

drop %-comment lines

GNL_TRIM

8

trim all lines

GNL_IGNORE_ALL

15

pass non-blank, non-comment lines and trim them

Returns the next line.

read

(LineReader_std and LineReader_gz)

uint read(void *pBuf, uint iSize);

Read iSize characters into pBuf.

pBuf

Buffer to read file contentrs into (must have a size of at least iSize bytes)

iSize

Number of bytes to read.

Returns number of bytes read.

seek

(LineReader_std and LineReader_gz)

int seek(long offset, int whence);

Move to a particular position in the file.

offset

Number of bytes to move.

whence

Starting point and direction:

SEEK_SET

move offset forward from the beginning of the file

SEEK_END

move offset backward from the end of the file

SEEK_CUR

move offset forward from the current position

tell

(LineReader_std and LineReader_gz)

long tell();

Returns the current position in the file.

isEoF

(LineReader_std and LineReader_gz)

bool isEoF();

Returns true if then of the file has been reached.

isReady

(LineReader_std and LineReader_gz)

bool isReady();

Returns true if the LineReader is ready.

Example

Compile with

g++ lr_example.cpp LineReader.cpp xha_strutils.cpp xha_strutilsT.h strutils.cpp --std=c++20 -lz -o lr_example

This example reads the lines of a file and prints the lines with a prepended line number.

Code for lr_example.cpp:

#include <cstdio>
#include <string>

#include "LineReader.h"

int main(int iArgC, char *apArgV[]) {
    if (iArgC > 1) {
        LineReader *pLR = LineReader_std::createInstance(apArgV[1], "rt");
        if (pLR != NULL) {
            int i = 1;
            char *pLine = pLR->getNextLine(GNL_IGNORE_NONE);
            while ((pLine != NULL) && (!pLR->isEoF())) {
                printf("[%05d] %s", i++, pLine);
                pLine = pLR->getNextLine(GNL_IGNORE_NONE);
            }

            delete pLR;
        }
    } else {
        printf("Usage: %s <text-file>\n", apArgV[0]);
    }
    return 0;

}