Storing text lines in an array, C

Question

I am new to C and I am confused how I can read through a file and store each line to an index of an array.

Example file:

What color is the sky?
Red
Orange
Yellow
Blue

Desired result of code:

input[0] = What color is the sky?
input[1] = Red
input[2] = Orange
input[3] = Yellow
input[4] = Blue

Hhere is what I have so far:

char input[60];

//declare string array of size 80, for 80 lines

for(int i = 0; fgets(input, sizeof(input), inFile)!=NULL; i++){ 

    //string[i] = input; storing this line to the string index

}

//later on use the string[80] that now has all lines

I understand that declaring input[60] is only determining the length of each line, not the number of lines. I am so used to thinking about strings in other coding languages, that the use of char is throwing me off. I have tried video tutorials but they didn't help me.

Answer 1

Each line of the file is a different string, and each string is a char* pointer to an array; so what you are needing is a 1D array of char* pointers (or alternately a 2D array of char.)

char *line[ MAX_LINES ];  // 1D array of char* pointers.

You can either initialize a two dimensional array of char, or you can malloc the memory for each line of the 1D char* pointers.

Here's an example of the malloc approach. The variable it's stored in is called "line" rather than "input"; but you can exchange the variable names if you like, and change the print formatting to solve your particular problem. This is just intended as an example of reading the strings into memory, in the same way you desire. No practical system has less than 4K of heap space, so I've omitted the malloc memory check.

#include <string.h>                                                             
#include <malloc.h>                                                             
#include <stdio.h>                                                              

#define MAX_LINES 10                                                            
#define MAX_LEN   60                                                            

int main( int narg, char *arg[] ) {                                             
    char input[ MAX_LEN ];                                                      
    char *line[ MAX_LINES ];                                                    
    FILE *inFile;                                                               
    int i,j;                                                                    

    if ( narg != 2 ){fprintf( stderr, "Use: %s filename\n", arg[0] ); return 2;}  
    if (!(inFile=fopen(arg[1],"r") )){
          fprintf( stderr, "Can't open '%s'\n",arg[1]);
          return 2;
    }

    for ( i=0; i<MAX_LINES && fgets(input, sizeof(input), inFile ); ++i ) {     
        int lineLen=strlen(input) + 1;                                          
        line[i] = strncpy( malloc( lineLen ), input, lineLen );                 
    }                                                                           

    for ( j=0; j<i; ++j ) { printf( "Line %d:%s", j+1, line[j] ); free(line[j]); }
    fclose(inFile);                                                             
    return 0;                                                                   
}