what is the segmentation fault?

[tefflox]

this is all that is given:

char word[10];
addS("fasten", word);
cout << endl << word << endl;  // will output fastens

for a program that must make a word plural (add an s)

here is my code, which compiles but gives a peculiar "segmentation fault" that I haven't seen before..

void addS(char [], char []);

int main() {

    char word[10];
    addS("fasten", word);
    cout << endl << word << endl;  // will output fastens    

    return 0;

} // main

void addS(char orig[], char plural[]) {
    
    int i;
    for(i = 0; true ; i++)
        plural[i] = orig[i];
        
    plural[i + 1] = 's';
    plural[i + 2] = '\0';

}// addS

I'm really lost on this. plz help.

[Dave Sinkula]

What ends this loop?

for(i = 0; true ; i++)

Nothing, it goes "forever", or until you crash.

[tefflox]

how about this, it gives "segmentation fault"

void addS(char [], char []);

int main() {
    
    char word[7]; 
    char singular[6];
    cout << "Input 6-letter word to make plural: ";
    cin >> singular;
    cout << singular << endl;
    addS(singular, word);
    cout << endl << word << endl;   

    return 0;

} // main

void addS(char orig[], char plural[]) {
    
    int i;
    for(i = 0; orig[i] != '\0' ; i++)
        plural[i] = orig[i];
    
    plural[i + 1] = 's';

}// addS

[GloriousEremite]

1. You're not leaving space for the '\0' terminator.
2. This line is wrong:

plural[i + 1] = 's';

3. The user could still enter more than 6 letters and cause a buffer overrun.

I'd recommend using a std::string instead. Or at least use getline to limit the number of characters entered.

[tefflox]

I'm not allowed to use anything besides char [] for this course. thx, i was just looking at that line and thought it should be plural = 's' but that doesn't work either...

[Dave Sinkula]

thought it should be plural = 's' but that doesn't work either...

It may if you null terminate the destination string.

[tefflox]

yes! thanks! this works..

void addS(char [], char []);

int main() {
    
    char word[8]; 
    char singular[7];
    cout << "Input 6-letter word to make plural: ";
    cin >> singular;
    singular[7] = '\0';
    addS(singular, word);
    cout << endl << word << endl;  // will output schools    

    return 0;

} // main

void addS(char orig[], char plural[]) {
    
    int i;
    for(i = 0; orig[i] != '\0' ; i++)
        plural[i] = orig[i];
    
[B]    plural[i] = 's';
    plural[i + 1] = '\0';[/B]

}// addS

[Dave Sinkula]

This is one beyond the array bounds:

singular[7] = '\0';

[tefflox]

note that i changed it so it's not beyond the array bounds. it's working now, thx

[Eddy Dean]

Taken from MSDN:

sizeof Operator  


Yields the size of its operand with respect to the size of type char.

Wouldn't this be usefull? It would probably save you a loop. It's also usefull to check if the user entered a 6-digit word.

Anyway, you made it, congratulations.

Greetz, Eddy

[Dave Sinkula]

Wouldn't this be usefull? It would probably save you a loop. It's also usefull to check if the user entered a 6-digit word.

I think you need to look at strlen .

[Eddy Dean]

I think you need to look at strlen .

I don't think that really matters. strlen is for strings only I guess, sizeof() can give the size of multiple variable types (Never really tried which types).

Anyway, he's got it working.

@the thread starter, to expand your program and learn a bit more you might also want to add support for words with more characters and don't add an "s" if the last character (before the /0) already is "s".

Greetz, Eddy

[Dave Sinkula]

How do you think sizeof would save a loop, or check the length of an entered string? String length may be different from array size.

[Eddy Dean]

You're right. sizeof() returns the array size, not the amount of characters in an array, and strlen only works for strings. You could of course convert the char to a string, but that's not the point here.

#include "stdafx.h"
#include <iostream>

using namespace std;

int main(int argc, char* argv[])
{
	char singular[6];
	cout << "Insert a word with max 6 characters to make plural: ";
	cin >> singular;
	char plural[7];
	sprintf(plural, "%ss", singular);
	cout << "The plural of " << singular << " is: " << plural << endl;
	return 0;
}

works fine too...

WARNING: INSERTING MORE THEN 6 CHARACTERS WILL RESULT IN A CRASH!

Greetz, Eddy