Thread: C programming challenge

Hey everyone!
The description of the program is on this page:
http://www.red-white.com/program.htm

I'm having problems with some functions.
I need some help how to do the 'append', 'update', and 'compact' functions.

Any help will be greatly appreciated.
Thank you in advance.

P.S. Just in case if it matters, this is to be run in Linux (gcc compiler).

I just do not know where to start yet.
I'm completely lost.

So far I have this:

------------ a3.c begins ---------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "diskdb.h"

int main(int argc, char**argv){

char choice;
int nColumns, i;
int colType;
table_hdr myHdr;
FILE* myFile;

myFile=fopen(argv[1], "r+");
if(myFile==NULL){
myFile=fopen(argv[1], "w+");
printf("Please input number of columns (max 6):\n");
do{
scanf("%d", &nColumns);
if(nColumns>6){
printf("Too many columns, try again:\n");
}
else if(nColumns<0){
printf("Too few columns, try again:\n");
}
}while((nColumns<0)||(nColumns>6));

/*while((colType>=0)&&(colType<3))*/

/*if((colType<0)||(colType>2)){
printf("Invalid data type, try again:\n");
}
else{*/
for (i=0;i<nColumns;i++){
printf("Enter type (0/INT, 1/FLO, 2/STR) and title for Column[%d]:", i);
scanf("%d %s", &colType, myHdr.title[i]);
printf("%d\n", colType);
if((colType<0)||(colType>2)){
printf("Invalid data type, try again:\n");
}
}
/*}*/
}
else{
fread(&myHdr, sizeof(myHdr),1,myFile);
}

switch(choice = menu()){
case 'a':
append(&myHdr, myFile);
break;
case 'b':
update(&myHdr, myFile);
break;
case 'd':
delete(&myHdr, myFile);
break;
case 'c':
compact(&myHdr, myFile);
break;
case 'p':
print(&myHdr, myFile);
break;
case 'q':
quit(&myHdr, myFile);
break;
default:
}

return 0;

}

------------ a3.c ends ---------------


------------ diskdb.c begins ---------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "diskdb.h"

char menu(){
char op;

printf("Data Base Utilities:\n");
printf("a: append a new record\n");
printf("u: update an existing record\n");
printf("d: delete a record\n");
printf("c: compact the database file\n");
printf("p: print the database file\n");
printf("q: quit the program\n");
printf("Please enter your choice: ");
scanf("%c", &op);
while (op == ' ' || op == '\n') scanf("%c", &op);
return op;
}

void quit(table_hdr* table, FILE* myFile){
fclose(myFile);
return;
}

void append (table_hdr* table, FILE* myFile){

return;
}

void update (table_hdr* table, FILE* myFile){

return;
}

void delete (table_hdr* table, FILE* myFile){

return;
}

void compact (table_hdr* table, FILE* myFile){

return;
}

void print (table_hdr* myHdr, FILE* myFile){

int i,j;

for (i=1;i<myHdr->cols;i++){
for (j=0;j<=20;j++){
printf("-");
}
printf("+");
}

return;
}

------------ diskdb.c ends ---------------


------------ diskdb.h begins ---------------
#define STRING_LEN 20
#define COLUMN 6
#define TITLE_LEN 20
typedef enum {INT, FLO, STR} datatype;

typedef struct {
datatype col_type[COLUMN];
int col_offs[COLUMN];
int cols;
int row_size;
char title[COLUMN][TITLE_LEN];
} table_hdr;

char menu();
int ftruncate( int, long );
int fileno( FILE * );
void append (table_hdr*, FILE* myFile);
void update (table_hdr*, FILE* myFile);
void delete (table_hdr*, FILE* myFile);
void compact (table_hdr*, FILE* myFile);
void print (table_hdr*, FILE* myFile);
void quit (table_hdr*, FILE* myFile);

------------ diskdb.h ends ---------------

I am stuck. Please help.

This looks like a hard one, but i will have a go, if you get a good answer yourself post something so that I don't waste too much time, we will get a doctorate out of this one for sure.

I almost got 'apend' and 'print' functions working.

Here's whatr I have:

void append (table_hdr* myTable, FILE* myFile){
/*-
The append function adds a row to a table.
It then writes the column data to the binary file at the end of the file.
-*/
int i;
int inInt;
float inFloat;
char inStr[STRING_LEN];

for (i=0;i<myTable->cols;i++){
printf("Input %s: ", myTable->title[i]);
if(myTable->col_type[i]==INT){
scanf("%d", &inInt);
fwrite(&inInt,sizeof(int),1,myFile);
}
else if (myTable->col_type[i]==FLO){
scanf("%f", &inFloat);
fwrite(&inFloat,sizeof(float),1,myFile);
}
else{
scanf("%s", inStr);
fwrite(&inFloat,sizeof(char)*STRING_LEN,1,myFile);
}

}
return;
}

void print (table_hdr* myTable, FILE* myFile){
/*-
This function prints the rows of the table.
-*/
int i,j;
for (i=0;i<myTable->cols;i++){
printf("%20s", myTable->title[i]);
if ((i+1)<myTable->cols){
printf("|");
}
}
printf("\n");
for (i=1;i<=myTable->cols;i++){
for (j=0;j<20;j++){
printf("-");
}
if (i<myTable->cols){
printf("+");
}
}
printf("\n");

return;
}

My print function won't print out the appended rows though. I'm trying to find out how to do it.
And in my output file I don't get what I should (1's and 0's) instead I get some crap. I think that there's a problem in my 'append' as well.

Can anybody help?