Problem with strcat

Hi, I have written a function called read_input and it is for writing a table of data from a file and categorizing and arranging them into an array of structs.. A sample of 1 line of the data is shown below:

1.1.1.1.2 = 1.2372e-05 23 4

The struct is written as:

struct database_input {
int category_A;
int category_B;
double category_C;
int category_D;
};

What I am intended to put into one of the index of the array is :

category_A = 11112
category_B = 23
category_C = 0.000012372
category_D = 4

My full written code is shown below:

Code:

void read_input( FILE *ifp, struct database_input *data)
{
int i=0;
char number = 0;
char *goto_A = NULL;

char  *category_C_f = NULL;
double goto_C;

char *goto_B;

while( i<99999 && feof(ifp) == 0)
	{
	while( number != ' ')
	{
		fscanf( ifp, &number);
		if (number != '.')
		strcat(goto_A, &number); //all of the strcat are making the segment faultation
	}

	data[i].category_A = (int)*goto_A;
	ifp = ifp+2;
	number = 0;

	while( number != 'e')
	{
		fscanf( ifp,&number);
		strcat(category_C_f, &number);
	}
	
	goto_C = (double)*category_C_f;
	data[i].category_C = goto_C/10000;
	ifp = ifp+5;
	number = 0;
	
	while( number != ' ')
	{
		fscanf( ifp, &number);
		if (number != '.')
		strcat(goto_B, &number);
	}

	
	data[i].category_B = (int)*goto_B;
	ifp = ifp+1;
	number = 0;
	fscanf( ifp, &number);
	data[i].category_D = (int)number;
	number = 0;
	
	while( number != '\n')
	{
		ifp++;
	}
	
	i++;
	}
}

Like what I had commented inside the code, I had a segmentation fault error when the code was run. This error was found (and has been later confirmed by a debugger) to be the fault of the strcat line, which I have been commented above. Can anybody please tell me how to fix this problem and tell me about other problems found in this program?

Thanks

Walk through the code and ask yourself this question:

What is the value of goto_A at

Code:

strcat(goto_A, &number);

That should tell you why it is failing.

If you still aren't sure, try outputting goto_A's value right before that bit of code.

Too slow !

Do you mean that I can't concatenate to a string when the string itself is Null?

Well, where would you be writing the second string to? You can't write to NULL. It's a place where there's guarenteed to be no valid memory to write to.

I have change the goto_A line to
char goto_A[] = "0"
and now I can strcat the first value, but whenever I have '.'(period) or ' '(space), the program crashes into a segmentation fault again.

How can I fix this problem?

Update: Instead of (fscanf( ifp, "%c", &number);), I used (number = fgetc(ifp);) and I also commented out (ifp++;).
I have tried different types of data, and it wouldn't stop when the space is read, and it keeps on reading until a segmentation fault occurs when it reads the equal sign.
Can somebody please help me on this problem?

char goto_A[] = "0"
allocates buffer of 2 chars

you should allocate buffer that will be big enough to store all the resulting string

Code:

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

struct database_input {
    int category_A;
    int category_B;
    double category_C;
    int category_D;
};

int main ( ) {
    char    input[] = "1.1.1.1.2 = 1.2372e-05 23 4\n";  // just like fgets() returns
    struct database_input foo;
    char    temp[6] = { 0 };
    if ( sscanf( input, "&#37;c.%c.%c.%c.%c = %lf %d %d",
                temp+0, temp+1, temp+2, temp+3, temp+4,
                &foo.category_C, &foo.category_B, &foo.category_D ) == 8 ) {
        foo.category_A = strtol( temp, NULL, 0 );
        printf( "Input=%s", input );
        printf( "A=%d, B=%d, C=%g, D=%d\n",
            foo.category_A, foo.category_B,
            foo.category_C, foo.category_D );
    }
    return 0;    
}

$ gcc foo.c
$ ./a.exe
Input=1.1.1.1.2 = 1.2372e-05 23 4
A=11112, B=23, C=1.2372e-05, D=4

Having done that, you can then do this

Code:

char input[BUFSIZ];
while ( fgets ( input, sizeof input, ifp ) != NULL ) {
  // now do the sscanf.
  // If the result isn't 8 (in this case), then report an error
}

hi guys, thanks for the reply, you guys are a great help, I have just rewritten the whole program by capturing the data into several strings, almost the same as you had there, but instead I did:
fscanf(ifp, "%s", a);

fscanf( ifp, "%s %s %d %d", equal, b, &c, &d);

and now it works perfectly. Again, thanks for you guys help and support.

Well until fscanf doesn't convert the number of expected values anyway...