Fill an array with strings from file

**niponki** · 07-31-2005

Ok, so I have been tasked with a simple assignment where I must write a program that creates an array of strings, where the number of rows is specified by the user. The program reads the data from input file and sorts the array by the last name.

This is what I have so far.

Code:

#include <stdio.h>
#include <stdlib.h>

//// PROTOTYPE DECLARATIONS ////
char **buildTable (void);
int readFile (void);

 

int main (void) //// BEGIN MAIN
{
	
	char **table = buildTable (); // <-CALL TO buildTable FUNCTION
	readFile(); // CALL TO readFile FUNCTION
	
	return 0;
}


char **buildTable (void)  //// BEGIN buildTable FUNCTION
{
	char **table;
	int rowNum, row;

	printf("Enter the number of rows in the table: \n");
	scanf("%d", &rowNum);
	table = (char **)calloc(rowNum +1, sizeof(char*));
	if(!table) return NULL;
	for (row = 0; row < rowNum; row++)
	table[row] = NULL;
	return table;
}

int readFile (void)  //// BEGIN readFile FUNCTION
{
	FILE *fpNames;

	if ((fpNames = fopen("lab4.txt", "r")) == NULL)
	{
	printf("\aERROR opening lab4.txt\n");
	return (100);
	
	
	}
	return 0;
}

So basically, I have a function to prompt the user to enter the amount of rows that he wants to see and that builds or allocates the memory for the array of strings. The next function opens the file and tests it to make sure it works. The question is this.

How do I read that file into the array of strings? I know that I have to make another function to fill the array, but I do not see how each module is going to communicate with each other.

Thanks in advance!!

**quzah** · 07-31-2005

You don't have to make another function. Just use fgets. The FAQ on getting a line from the user covers its use.

Quzah.

**niponki** · 07-31-2005

Ok, I have been doing some more reading, and I know how to initialize a string. For example,

Code:

string1[] = "Monday";

That would initialize an array called string1 that is filled with a string, "Monday". Is this correct? If this is the case, can I do the same thing by putting the file pointer in the quotes, so that it would read from the file? For example, could I do this

Code:

string2[] = "*fpFileName";

Would this read from the file, FileName, or would it just put the letters *fpFileName into the string? I am guessing the latter, but hoping the first. hehe.

**niponki** · 07-31-2005

oOh ok.. I will try that out and see what I come up with. Thanks!!

**niponki** · 07-31-2005

Ok, so i modified the readfile function of my program with the fgets command and compiled it with no errors. Is there anyway to test my program to make sure that the file really is being read into string? Like, can I print something to the screen (print the file to the screen) to check to make sure it works. In theory, I would think at least, is that once the file is read into the string, I can just print the string to the screen with a "sprintf" function. Probrally totally wrong, but i guess it doesn't hurt to ask.

Anyway, here is the modified function:

Code:

int readFile (void)  //// BEGIN readFile FUNCTION
{
	char str [80];
	FILE *fpNames;

	if ((fpNames = fopen("lab4.txt", "r")) == NULL)
	{
	printf("\aERROR opening lab4.txt\n");
	return (100);	
	
	}
	fgets(str, sizeof (str), stdin);

	return 0;
}

**niponki** · 07-31-2005

ok, so after a little more research, i can easily see that this last post was pretty stupid... i think... so my fgets and my str[] array are not linked in anyway. i just don't understand the syntax that is needed to get these two guys to talk to eachother. HELP!! =) Thank you!!

**niponki** · 07-31-2005

so i am going to take make a function call from the readfile function to fill the array. I know how to fill the array, and I know how to fill and array of strings, but i do not know how to do it from a file. any help?

**dwks** · 07-31-2005

Use fgets() with your file pointer.

**niponki** · 07-31-2005

I'm sorry, I am still not 100% understanding this. This is what I know I have to do. I know I have a function that reads a file, then calls another function to fill an array with that file. This array will be an array of strings seeing that the file is a list of names. I know I have to use the fgets() with the file pointer, but maybe i can't seem to make it all come together. Thanks.

Here is my code so far if it helps:

Code:

#include <stdio.h>
#include <stdlib.h>

#define MAXELEMS 80

//// PROTOTYPE DECLARATIONS ////
char **buildTable (void);
int readFile (void);
char fillAry (void);

 

int main (void) //// BEGIN MAIN
{
	
	char **table = buildTable (); // <-CALL TO buildTable FUNCTION
	readFile(); // CALL TO readFile FUNCTION
	
	return 0;
}


char **buildTable (void)  //// BEGIN buildTable FUNCTION
{
	char **table;
	int rowNum, row;

	printf("Enter the number of rows in the table: \n");
	scanf("%d", &rowNum);
	table = (char **)calloc(rowNum +1, sizeof(char*));
	if(!table) return NULL;
	for (row = 0; row < rowNum; row++)
	table[row] = NULL;
	return table;
}

int readFile (void)  //// BEGIN readFile FUNCTION
{

	FILE *fpNames;

	if ((fpNames = fopen("lab4.txt", "r")) == NULL)
	{
	printf("\aERROR opening lab4.txt\n");
	return (100);	
	
	}
	fillAry (); //// <-- CALL TO fillAry FUNCTION	

	return 0;
}

char fillAry (void)
{

// Here is where I want to fill the array with the strings from the input file with fgets().

}

**quzah** · 07-31-2005

You still aren't allocating anything for each row. You'll have to do that in 'fillAry' I suppose. Something like:

Code:

void fillAry( char ** yourlist, size_t numrows )
{
    char buf[BUFSIZ] = {0};
    FILE *fp;
    size_t row = 0;

    fp = fopen( "yourfile", "r" );

    while( fgets( buf, BUFSIZ, fp ) !=  NULL && row < numrows )
    {
        size_t len = strlen( buf );
        yourlist[ row ] = malloc( len );
        strncpy( yourlist[ row ], buf, len - 1 );
    }
}

That looks about right. Potentailly a few minor annoying bugs, since I didn't do any error checking, but I'll leave that up to you. Oh, and you really should call free for each row of your array when you're all done. Plus you'll have to free the whole works then too. Oh, and close your file when you're done with it.

[edit]
Oh, and if you want to see if it's reading correctly, just do a quick run through:

Code:

void readfile( void )
{
    char buf[BUFSIZ] = {0};
    FILE *fp;

    fp = fopen( "yourfile", "r" );

    while( fgets( buf, BUFSIZ, fp ) != NULL  )
    {
        printf("This buffer contains: %s\n", buf );
    }
    fclose( fp );
}

Again, do some error checking.
[/edit]

Quzah.

**itsme86** · 08-01-2005

Code:

    while( fgets( buf, BUFSIZ, fp ) !=  NULL && row < numrows )
    {
        size_t len = strlen( buf );
        yourlist[ row ] = malloc( len );
        strncpy( yourlist[ row ], buf, len - 1 );
    }

I do believe that's leaving the stored strings unterminated. You'll have to do something like this after the strncpy():

Code:

yourlist[row][len - 1] = '\0';

**quzah** · 08-01-2005

Originally Posted by itsme86

I do believe that's leaving the stored strings unterminated. You'll have to do something like this after the strncpy():

Code:

yourlist[row][len - 1] = '\0';

From the man page:

The strncpy() function is similar, except that not more than n bytes of
src are copied. Thus, if there is no null byte among the first n bytes
of src, the result will not be null-terminated.

Ack. Too tired. Yeah, I was thinking it was the other way around. Guess I was thinking of strcpy.

Quzah.

**niponki** · 08-01-2005

hey thanks a lot for your help guys. I am going to keep working on it and I will let you know i can get it done!! again, i really appreciate it!!

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