C How to make a list of messages? - c

Question

I would like to make a list of messages witch I call by an index number. So I would get the input 13, then message 13 should be printed. My issue is that I need a lot of theses messages and they need to be of multiple lines, this would take up to much space in my main file. So my question is how do I store all these messages and call them when needed?

Answer 1

I would store them in a separate source file in an array of char*. The number can simply be an index into the array.

Answer 2

According to my understanding of your question. You should use array of string. because array is the fastest way of storing and retrieving data. you may use like below:
char a[2][1000];
strcpy(a[0], "I hello how r u");
strcpy(a[1], "i m fine");
You can access messages by index of array. if you want access first message then you will get by a[0],for second message a[1], for third a[2] and so on.

Answer 3

A simple approach
char const * getMessageByIndex( int const index ) {
static char const * const messages[] = {
"I am message 0",
"I am message 1",
// ...
};
int const numMessages = sizeof messages / sizeof messages[ 0 ];
if( (index < 0) || (numMessages <= index) {
// error handling
return "index out of bound";
}
return messages[ index ];
}

Answer 4

make index file and message file. and message read by index file.
e.g.)*Error handling is omitted.
make index and message file:
#include <stdio.h>
const char* message[] = {
"1st message",
"2nd message\ninclude newline",
"3rd message"
//...
};
int main(){
FILE *indexFile, *textFile;
long loc=0;
int i, size, len;
size=sizeof(message)/sizeof(char*);
indexFile=fopen("index.dat", "wb");
textFile=fopen("message.dat", "wb");
for(i=0;i<size;++i){
loc = ftell(textFile);
fwrite(message[i], sizeof(char), len=strlen(message[i]), textFile);
fwrite(&loc, sizeof(long), 1, indexFile);
fwrite(&len, sizeof(int), 1, indexFile);
}
fclose(textFile);
fclose(indexFile);
return 0;
}
use sample:
#include <stdio.h>
#include <stdlib.h>
char* readMessage(int n){
char *message;
FILE *indexFile, *textFile;
long loc;
int i, size, len;
int recordSize = sizeof(long) + sizeof(int);
indexFile=fopen("index.dat", "rb");
textFile=fopen("message.dat", "rb");
loc = recordSize * n;
fseek(indexFile, loc, SEEK_SET);
fread(&loc, sizeof(long), 1, indexFile);
fread(&len, sizeof(int ), 1, indexFile);
message=(char*)malloc(sizeof(char)*(len+1));
fseek(textFile, loc, SEEK_SET);
fread(message, sizeof(char), len, textFile);
message[len]='\0';
fclose(textFile);
fclose(indexFile);
return message;
}
int main(){
char *mes;
int n;
n =1;
mes = readMessage(n);//zero origin
printf("message %d is \"%s\"\n", n, mes);
free(mes);
return 0;
}