C: Reading a file into an array

Question

I have a text file and i want to to read it line by line and put the lines into an array.

The snippet behind gives error while compiling:

FILE *f;
char line[LINE_SIZE];
char *lines;
int num_righe;

f = fopen("spese.dat", "r");

if(f == NULL) {
    f = fopen("spese.dat", "w");
}

while(fgets(line, LINE_SIZE, f)) {      
    num_righe++;
    lines = realloc(lines, (sizeof(char)*LINE_SIZE)*num_righe);
    strcpy(lines[num_righe-1], line);
}

fclose(f);

The error is:

spese.c:29: warning: assignment makes integer from pointer without a cast
spese.c:30: warning: incompatible implicit declaration of built-in function ‘strcpy’
spese.c:30: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast

Any help? Thanks

you should really include the header #include <string.h> into your program. Good that you haven't done -fno-builtin, in which case it could not have warned you and the program would have silently been compiled by gcc. — Johannes Schaub - litb
– Johannes Schaub - litb, Commented May 4, 2009 at 19:41
I'm dubious about the value of the if (!f) fopen("spese.dat", "w"); part. If that condition happens, f is open for write, and fgets() cannot succeed. Also a little more error checking would be a good thing throughout, especially of realloc() where it will return NULL on failure without freeing the old buffer. — RBerteig
– RBerteig, Commented May 5, 2009 at 0:53

Emil H · Accepted Answer · 2009-05-04 19:41:03Z

5

Try:

FILE *f;
char line[LINE_SIZE];
char **lines = NULL;
int num_righe = 0;

f = fopen("spese.dat", "r");

if(f == NULL) {
        f = fopen("spese.dat", "w");
}

while(fgets(line, LINE_SIZE, f)) {              
        num_righe++;
        lines = (char**)realloc(lines, sizeof(char*)*num_righe);
        lines[num_righe-1] = strdup(line);
}

fclose(f);

answered May 4, 2009 at 19:41

Emil H

40.3k11 gold badges81 silver badges97 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Tom Over a year ago

isn't sizeof(char) always identical to 1 byte?

Emil H Over a year ago

Yes. But my code uses sizeof(char*) which in general is 4 bytes, not 1.

Tom Over a year ago

Oh, didn't notice that *. I apologize.

Emil H Over a year ago

Don't worry about it. Can happen to anyone. :)

Tom Over a year ago

Actually, strdup CAN return NULL. You might want to take that into account. In addition to that, you should remember to free that memory once you are done (strdup uses malloc)

Tom · Accepted Answer · 2009-05-04 19:53:55Z

2

I take this is a code snipet, consequently, i guess that you are alredy including string.h

strcpy is defined as:

  char * strcpy ( char * destination, const char * source );

In

 strcpy(lines[num_righe-1], line);

lines [num_righe-1] is a char, not a char*

So it should be

strcpy(lines + (num_righe-1), line);

As munificent wrote, it looks like you are trying to make lines an array of strings. If so, your definition of lines is wrong.

Also, dont forget, you should check that realloc doesn't return NULL.

lines = realloc(lines, (sizeof(char)*LINE_SIZE)*num_righe);

if (!lines) //MUST HANDLE NULL POINTER!!

/* string copy code here*/

edited May 4, 2009 at 19:53

answered May 4, 2009 at 19:34

Tom

45.4k30 gold badges142 silver badges171 bronze badges

4 Comments

foobarfuzzbizz Over a year ago

Aren't these statements identical?

Emil H Over a year ago

No. lines[num_righe-1] is a char, and lines + (num_righe-1) is a pointer to the same char. One could also use &lines[num_right-1].

anon Over a year ago

There is no need to cast when using realloc.

Tom Over a year ago

@Neil. I was dubitative about that one. It's gone.

munificent · Accepted Answer · 2009-05-04 19:34:56Z

1

lines is a pointer to a character, i.e. a single string. You want it to be an array of strings. For that, it should be char **lines;

answered May 4, 2009 at 19:34

munificent

12.4k4 gold badges42 silver badges56 bronze badges

Comments

foobarfuzzbizz · Accepted Answer · 2009-05-04 19:35:15Z

1

You can use fscanf instead to do what you want.

fscanf(f, "%s\n", line[index]);
index++;

answered May 4, 2009 at 19:35

foobarfuzzbizz

59.1k57 gold badges148 silver badges198 bronze badges

Collectives™ on Stack Overflow

C: Reading a file into an array

4 Answers 4

5 Comments

4 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

5 Comments

4 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related