How to replace text file and use an array instead?

Feb 21, 2011 at 11:15pm
sharris (21)
Hello Everybody,

This program works and it use a text file named yes.txt with these lines and no blank line at the beginning or end of file:
sing
Sing
SANG!!!
yes
no
nope YES nope YES

Now that I know how to work with vector a bit I want to eliminate this external file and do the same thing with the same text being inside the program in a string array mainly for the knowledge of how-to. I thought it would be simple, I included a array "string zfile[6]" to replace the external text file but I don't know how to make it work using this array. Could someone show me the syntax to use to make this happen. I'm hoping to stay close as possible to what I already have so that I can understand the changes that will be needed ... or do the entire set-up has to be changed completly. Thanks in advance


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#include <iostream>
#include <fstream>
#include <string>
#include <vector>

using namespace std;

string zfile[6]={"sing", "Sing", "SANG!!!", "yes", "no", "nope YES nope YES",};
//string zfile[6];


int main()
  {
     ifstream xfile("yes.txt");

        if ( !xfile )
        {     cerr << "File does not exist.\n\n"; system("pause");  exit( 1 );  }

        vector<string> lines;
        string line;

        while (getline(xfile, line))
        {
        lines.push_back(line);
                                
        cout << "results:  " <<  line  << endl;
        }

        xfile.close();

        system("pause");

 }
Edit & run on cpp.sh
Feb 21, 2011 at 11:22pm
PanGalactic (1658)
To use your array of strings, you can initialize lines like so:
 
 
vector<string> lines(zfile, zfile + 6);


Is that what you are asking?
Last edited on Feb 21, 2011 at 11:23pm
Feb 22, 2011 at 12:59am
sharris (21)
Is that what you are asking?


I mainly need to know how to do this using C and C++ standard string libraries for given array of strings. This will leave me with a clear understanding of how to switch back and forth from external files usage to an internal arrays of strings when needed for difference types of coding project.

I will certainly be trying this Array of vector<string> in a few minutes which is a BIG PLUS. :) But I don't need to get to fancy with vector just yet. I just want to end-up using the most fail-proof method possible. C++ people say use C++ strings but if C-strings are safer I am not so lazy or afraid to work with them but if vector is the the way to go than I will dedicate my all into it. Give me the word and I am there.

But for now it's all about how to translate the code from using an external file to using a build-in arrays. While googling I found that many people need help to do just the reverse of what I am after. Thanks a lot for the reply. I can't wait to try it ...
Feb 22, 2011 at 1:36am
sharris (21)
PS: After just doing more googling, I think my exampe may be mis-leading, but I hope many of you still get my point. Another thing I am a noob and I don't know how to insert this vector<string> lines(zfile, zfile + 6); thing yet and other changes needed. It's a lot more to it than I thought.

Thanks again
Feb 22, 2011 at 3:44am
sharris (21)
Got it!!!
Google and the pages here is the GREATEST :)

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#include <iostream>
#include <string>
#include <vector>
using namespace std;


void ShowTime (const vector<string>& j)
     {
     for (int i = 0; i < j.size(); ++i)
     {
     cout << "  " << j[i] << endl;    }   }

int main ()
    {
    vector<string> str1(10);
    cout << endl << endl;
    str1[0] = "sing_C++";
    str1[1] = "sing";
    str1[2] = "Sing_C++";
    str1[3] = "or";
    str1[4] = "to";
    str1[5] = "the";
    str1[6] = "slammer";
    str1[7] = "you";
    str1[8] = "GO!";   
    str1[9] = " ";
                 ShowTime (str1);

    vector<string> str2;// vector with size zero, will grow to accommodate

    str2.push_back(" ");
    str2.push_back("la");
    str2.push_back("la");
    str2.push_back("la");
    str2.push_back("lalalaaaa");
                 ShowTime (str2);

    cout << endl << endl;

system("pause");
system ("CLS");
//return main();
}
Edit & run on cpp.sh


This is pure C++... Now how would I do it in pure C ...
Feb 22, 2011 at 9:52am
krishnendu (36)
You have to write the string and vector classes from scratch. I have made some effort, but it is laborious :(

main.h
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#ifndef __MAIN__
#define __MAIN__

/************ Implementation of std::string<char> in C ***********/

struct String
{
	char *elements;
};

void String_constructor (struct String *this);
void String_copyConstructor (struct String *this, const struct String *o);
void String_destructor (const struct String *this);
int String_size (const struct String *this);
const char *String_get (const struct String *this);
void String_assign (struct String *this, const char *str);

/************ Implementation of std::vector<std::String> in C ***********/

struct StringVector
{
	struct String *elements;
	size_t size;
	size_t capacity;
};

void StringVector_constructor (struct StringVector *this);
void StringVector_destructor (const struct StringVector *this);

size_t StringVector_push_back (struct StringVector *this,
			       const struct String *string);

const struct String *StringVector_getElement (const struct StringVector *this,
					      size_t i);

size_t StringVector_size (const struct StringVector *this);

#endif


main.c
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "main.h"

/************ Implementation of std::string<char> in C ***********/
/********** Constructor/Destructor ***********/

void String_constructor (struct String *this)
{
	printf ("%p: String_constructor\n", this);
	this->elements = malloc (1);
	strcpy (this->elements, "");
}

void String_copyConstructor (struct String *this, const struct String *o)
{
	printf ("%p: String_copyConstructor: from %p\n", this, o);
	this->elements = malloc (strlen (o->elements) + 1);
	strcpy (this->elements, o->elements);
}

void String_destructor (const struct String *this)
{
	printf ("%p: String_destructor\n", this);
	free (this->elements);
}

/********** Capacity ***********/

int String_size (const struct String *this)
{
	return strlen (this->elements);
}

/********** Element access ***********/

const char *String_get (const struct String *this)
{
	return this->elements;
}

/********** Modifier ***********/

void String_assign (struct String *this, const char *str)
{
	printf ("%p: String_assign: %s\n", this, str);
	this->elements = (char *)realloc (this->elements, strlen(str) + 1);
	strcpy (this->elements, str);
}

/************ Implementation of std::vector<std::String> in C ***********/
/********** Constructor/Destructor ***********/

void StringVector_constructor (struct StringVector *this)
{
	printf ("%p: StringVector_constructor\n", this);
	this->elements = malloc (1);
	this->size = 0;
	this->capacity = 1;
}

void StringVector_destructor (const struct StringVector *this)
{
	size_t i;
	printf ("%p: StringVector_destructor\n", this);

	for (i = 0; i < this->size; i++)
		String_destructor (&this->elements[i]);

	free (this->elements);
}

/********** Modifier ***********/

size_t StringVector_push_back (struct StringVector *this,
			       const struct String *string)
{
	size_t i;
	struct String *relocatedElements;
	printf ("%p: StringVector_push_back\n", this);

	if (this->size == this->capacity) {

		printf ("%p: StringVector_push_back: re-allocating\n", this);
		this->capacity = 2 * this->capacity;

		relocatedElements = (struct String *)
		malloc (this->capacity * sizeof (struct String));

		for (i = 0; i < this->size; i++)
			String_copyConstructor (&relocatedElements[i],
						&this->elements[i]);

		for (i = 0; i < this->size; i++)
			String_destructor (&this->elements[i]);

		free (this->elements);
		this->elements = relocatedElements;

		printf ("%p: StringVector_push_back: re-allocation complete\n",
			this);
	}

	String_copyConstructor (&this->elements[this->size], string);
	this->size++;
}

/********** Element access ***********/

const struct String *StringVector_getElement (const struct StringVector *this,
					      size_t i)
{
	return &this->elements[i];
}

/********** Capacity ***********/

size_t StringVector_size (const struct StringVector *this)
{
	return this->size;
}

/********************* Main program ***********************/

void showTime (const struct StringVector *vector)
{
	size_t i;

	for (i = 0; i < StringVector_size (vector); i++)
		printf ("%s\n",
		String_get (StringVector_getElement (vector, i)));
}

int main (void)
{
	struct StringVector stringVector;
	StringVector_constructor (&stringVector);

	struct String str1;
	String_constructor (&str1);
	String_assign (&str1, "Hi");
	StringVector_push_back (&stringVector, &str1);
	String_destructor (&str1);

	struct String str2;
	String_constructor (&str2);
	String_assign (&str2, "Hello");
	StringVector_push_back (&stringVector, &str2);
	String_destructor (&str2);

	showTime (&stringVector);
	StringVector_destructor (&stringVector);
	return 0;
}
Edit & run on cpp.sh


The output goes as:


0xbf9b2704: StringVector_constructor
0xbf9b2700: String_constructor
0xbf9b2700: String_assign: Hi
0xbf9b2704: StringVector_push_back
0x806d008: String_copyConstructor: from 0xbf9b2700
0xbf9b2700: String_destructor
0xbf9b26fc: String_constructor
0xbf9b26fc: String_assign: Hello
0xbf9b2704: StringVector_push_back
0xbf9b2704: StringVector_push_back: re-allocating
0x806d038: String_copyConstructor: from 0x806d008
0x806d008: String_destructor
0xbf9b2704: StringVector_push_back: re-allocation complete
0x806d03c: String_copyConstructor: from 0xbf9b26fc
0xbf9b26fc: String_destructor
Hi
Hello
0xbf9b2704: StringVector_destructor
0x806d038: String_destructor
0x806d03c: String_destructor


Watch the pointers to carefully to track how the classes/structures are created, copied and destroyed.
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