creating a dynamically allocated array of strings from a file

[gucci09]

I was wondering how you would go about creating a dynamically allocated array of strings from a file. i have a dictionary that i want to load in my program in order to spell check. i cant decide if it is best to use an array of string pointers or an array of the actual words. also i am very new to C and really am not comfortable with malloc yet. any help would be greatly appreciated

[Silent1Mezzo]

I was wondering how you would go about creating a dynamically allocated array of strings from a file. i have a dictionary that i want to load in my program in order to spell check. i cant decide if it is best to use an array of string pointers or an array of the actual words. also i am very new to C and really am not comfortable with malloc yet. any help would be greatly appreciated

Unfortunately in C there is no really easy way of doing this. The easiest way I can think of off the top of my head is to have a double pointer.

char **ptr;

I would get really comfortable with malloc because you're going to be using it alot. Since the size of the string can fluctuate and you want a dynamic number of these strings you basically need to have a double pointer.

[gucci09]

thanks for the suggestion. so if i was going to use a double pointer would i malloc space for the rows and columns separately or can you do it together? again im not good with malloc. also i am trying to read this dictionary from one that is already on my system. so how would i determine how big to malloc space based on how many words are in this dictionary. i would just go look at it but my boss's dictionary might be different because he has an older version of ubuntu. so ya i guess would also be helpful to know to be able to put this dictionary in this program.

[Silent1Mezzo]

thanks for the suggestion. so if i was going to use a double pointer would i malloc space for the rows and columns separately or can you do it together? again im not good with malloc. also i am trying to read this dictionary from one that is already on my system. so how would i determine how big to malloc space based on how many words are in this dictionary. i would just go look at it but my boss's dictionary might be different because he has an older version of ubuntu. so ya i guess would also be helpful to know to be able to put this dictionary in this program.

I'm not that great with pointers but I believe you have to do something like this

char **ptr;
*ptr = malloc(sizeof(ptr) + 1);
ptr = malloc(sizeof(dictionaryLine) + 1);
 

Basically you allocate room for one more line and then you malloc room for the length of the line.

[gucci09]

cool thanks. so is that for just one line? like say the dictionary has 40000 words in it. but i really dont know how many there are. how do i check for the amount of lines/words/strings the dictionary contains inorder to put that in my malloc. like can i loop to the end of the file and count them or how do i do that. this is the first time ive been asked to program something that opens other files and such.

[ilikepython]

I'm not that great with pointers but I believe you have to do something like this

char **ptr;
*ptr = malloc(sizeof(ptr) + 1);
ptr = malloc(sizeof(dictionaryLine) + 1);
 

Basically you allocate room for one more line and then you malloc room for the length of the line.

I don't think that's correct.
I believe it is like this:

char **ptr;
ptr = malloc(rows * sizeof(int *));
for (int x = 0; x < rows; x++)
{
   ptr[x] = malloc(columns * sizeof(int))
}
 

[Savage]

I don't think that's correct.
I believe it is like this:

char **ptr;
ptr = malloc(rows * sizeof(int *));
for (int x = 0; x < rows; x++)
{
   ptr[x] = malloc(columns * sizeof(int))
}
 

ilikepython is correct except that he forgot to cast them to char pointers.Rememeber:

void *malloc(size_t size);

this is malloc declararation.

So it should be:

char **ptr;
ptr = (char**)malloc(rows * sizeof(int *));
for (int x = 0; x < rows; x++)
{
   ptr[x] = (char*)malloc(columns * sizeof(int))
}
 

Savage

[gucci09]

hey thanks you guys...but how do i know how big the rows and columns are based on the dictionary file i have?

[Savage]

hey thanks you guys...but how do i know how big the rows and columns are based on the dictionary file i have?

Well you have a file after all.How do you read data from file?You could just add a variable that will count how many lines is there in file and then that would be rows,for columns there are two options:

1.Build another dynamilcy array that will keep track of the everyline length

2.Find the longest line and make every column of same size

Savage

[gucci09]

see i guess that is my question though. maybe i am dumb but i dont know how to count lines in a file. like i guess i could make a variable called 'counter' but how do i increment that so it skips a line. i hope i dont sound too retarded but i really am new to this and my boss wants this done soon. as you can see i am working on it from home now just so i can see if i can get it done.

[Savage]

see i guess that is my question though. maybe i am dumb but i dont know how to count lines in a file. like i guess i could make a variable called 'counter' but how do i increment that so it skips a line. i hope i dont sound too retarded but i really am new to this and my boss wants this done soon. as you can see i am working on it from home now just so i can see if i can get it done.

You are reading in a line using fgets(),right?

So u have a while loop with condition:

!feof(FILE *pointer) or something like this

every time that fgets makes a read,you increase your row counter


Savage

[gucci09]

so i am still having the same problem. here is my code. i keep getting a seg fault.

s=(char **)malloc(1*sizeof(char*));
        s[0]=(char *)malloc(strlen(s[i]));
 
        i++;
 
 
    while(!feof(finptr)){
        s=(char **)realloc(s,i*sizeof(char*));
        s[i]=(char *)realloc(s[i],strlen(s[i]));    
    }

[Savage]

so i am still having the same problem. here is my code. i keep getting a seg fault.

s=(char **)malloc(1*sizeof(char*));
        s[0]=(char *)malloc(strlen(s[i]));
 
        i++;
 
 
    while(!feof(finptr)){
        s=(char **)realloc(s,i*sizeof(char*));
        s[i]=(char *)realloc(s[i],strlen(s[i]));    
    }

Have you freed the memory?

Savage

[gucci09]

i free it at the end of my program i just copied a part of it. but now when i go thru the code it only lets me copy 3 words into my 's' string. once i=3 then it seg faults. i dunno whats going on. ill copy the whole code this time.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
 
int main(int argc, char *argv[]){
 
    FILE *finptr;        //file pointer to input file
 
    int i=0;        //for incrementing
    int loweraddress;    //lower address of file stored in array
    int upperaddress;    //upper address of file stored in array
    int counter=0;        //counts how many strings in file    
    char **s;        //pointer to character sting
    char hold[]="Conspiracy Theory's are cool!";
 
 
/*-------------------------------------------------------------------------------*/
//test for too few arguements    
    if(argc<2){
        printf("\nToo few arguements \n");
        printf("Usage: <program> <input file> \n");
        return 0;
    }
 
//test for too many arguements
    if(argc>2){
        printf("\nToo many arguements \n");
        printf("Usage: <program> <input file> \n");
        return 0;
    }
 
//test to see if input file can be opened and open it
    if((finptr=fopen(argv[1],"rt"))==NULL){
        printf("\n Cannot open input file \n");
        return 0;
 
    }
 
//malloc array and copy in words
 
        if((s=(char **)malloc(1*sizeof(char*)))==NULL){
            printf("malloc failed\n");
        }
        fgets(hold,100,finptr);
        s[i]=(char *)malloc(strlen(hold));
        strcpy(s[i],hold);
        printf("%s \n",s[i]);
 
 
        i++;
 
 
    while(!feof(finptr)){
        if((s=(char **)realloc(s,i*sizeof(char*)))==NULL){
            printf("malloc failed \n");
        }
        fgets(hold,100,finptr);
        s[i]=(char *)realloc(s[i],i*strlen(hold));
        strcpy(s[i],hold);
        printf("%s \n",s[i]);
        i++;
 
 
    }
 
    printf("%d - %d \n", &s[0], &s[i]);
/*----------------------------------------------------------------------------------*/
 
 
 
 
 
 
 
 
 
free(s);
return 0;
}

[Savage]

With this line here,you allocate only enough memory for 4 char *:

if((s=(char **)malloc(1*sizeof(char*)))==NULL){

Sizeof char* is 4,so when i goes over 3...seg error.

You will need to check first the file length and then allocate memory

Savage

[gucci09]

alright i changed my code around now bc i decided i dont need a 2 dimentional array. what am i doing wrong?

//calculate array size
 
        while(i!= EOF){
            i=fgetc(finptr);
            counter++;
        }            
 
//malloc array and copy in words
        s=(char *)malloc(counter);
 
        i=0;
        while(i<counter){
            fscanf(finptr,"%c",&s[i]);
            printf("%c", s[i]);
            i++;
        }
//store address of array    
    loweraddress=(int)&s[0];
    upperaddress=(int)&s[counter];
 
 
 

basically the characters are not being copied in
and i dunno if the address are working right either

[weaknessforcats]

//malloc array and copy in words
s=(char *)malloc(counter);

i=0;
while(i<counter){
fscanf(finptr,"%c",&s[i]); <<<<<<<<
printf("%c", s[i]);
i++;
}

You need to allocate memory for s[i] before you copy to it.