Reading a null terminated string from a binary file c++

Question

As the title says I'm trying to read a null terminated string from a binary file.

std::string ObjElement::ReadStringFromStream(std::ifstream &stream) {
    std::string result = "";
    char ch;
    while (stream.get(ch) != '\0') {
        result += ch;
    }
    return result; }

My null character is '\0'

But any time I call the method it reads to the end of the file

std::ifstream myFile(file, std::ios_base::in | std::ios_base::binary);
myFile.seekg(startByte);

this->name = ObjElement::ReadStringFromStream(myFile);

Any idea what I'm doing wrong here?

You don't need to provide ios::in or set empty string to "" explicitly. — Neil Kirk
– Neil Kirk, Commented Aug 8, 2014 at 14:58
im not reading from the start of the file, I have the start byte I need from somewhere else. — user1711383
– user1711383, Commented Aug 8, 2014 at 15:00
Are you sure the file contains the ASCII Zero character in it? How did you get/create the file? — jmucchiello
– jmucchiello, Commented Aug 8, 2014 at 15:00

jotik · Accepted Answer · 2017-09-16 13:56:44Z

9

Use std::getline:

#include <string> // for std::getline

std::string ObjElement::ReadStringFromStream(std::ifstream &stream) {
    std::string s;
    std::getline(stream, s, '\0');
    return s;
}

edited Sep 16, 2017 at 13:56

answered Aug 8, 2014 at 15:00

jotik

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2 Comments

Drew McGowen Over a year ago

Please leave a comment when downvoting.

Hugo Over a year ago

This comment gives a straightforward implementation of the question in the title, but it does not answer the 'Why does my code fail question' related to the body of the question. Answering the title helped me most.

Remy Lebeau · Accepted Answer · 2014-08-08 17:16:21Z

6

istream::get(char &) returns a reference to the istream, not the character read. You can either use the istream::get() variant like so:

while ((ch = stream.get()) != '\0') {
    result += ch;
}

Or use the returned stream reference as a bool:

while (stream.get(ch)) {
    if (ch != '\0') {
        result += ch;
    } else {
        break;
    }
}

edited Aug 8, 2014 at 17:16

Remy Lebeau

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answered Aug 8, 2014 at 15:00

Drew McGowen

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Comments

Igor Pejic · Accepted Answer · 2014-08-08 15:00:38Z

4

Use getline and pass \0 (null character) as the delimiter.

answered Aug 8, 2014 at 15:00

Igor Pejic

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2 Comments

Neil Kirk Over a year ago

Could the downvoter explicitly explain why this wouldn't work?

user1711383 Over a year ago

yeah, this is easier than my way of doing it. upvoted

Steve Fallows · Accepted Answer · 2014-08-08 15:00:27Z

1

The get() function returns a reference to the stream , not the character which has been put in ch .

You need to test ch for being a '\0'.

answered Aug 8, 2014 at 15:00

Steve Fallows

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1 Comment

user1711383 Over a year ago

ahhhh I see what I've done. Thats probably it alright

Massimo Costa · Accepted Answer · 2014-08-08 15:04:40Z

0

The get function returns the reference of the stream not the read character.

Modifiy the code like:

std::string ObjElement::ReadStringFromStream(std::ifstream &stream) {
    std::string result = "";
    while (stream.get(ch)) { // exit at EOF
        if (ch != '\0')
            result += ch;
        else
            break;  // Stop the loop when found a '\0'
    }
    return result; 
}

answered Aug 8, 2014 at 15:04

Massimo Costa

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