c gtk+: loading a text file into a GtkSourceView's TextBuffer

Question

I'm writing a program using the C language with gtk+ and gtksourceview-2.0.

I'm using a GtkFileChooser for the user to choose a file and when he clicks on it, i want the content to be loaded to the GtkSourceView' TextBuffer

this is the function that gets executed when a user double click's a file on the GtkFileChooser:

void on_file_activated(GtkWidget *widget, gpointer data) {
    GFile *file;
    FILE *fp;
    gchar *path_name;
    long file_size;
    gchararray file_buffer;
    file = gtk_file_chooser_get_file(GTK_FILE_CHOOSER(widget));
    path_name=g_file_get_path(file);
    g_debug("%s is chosen\n", path_name);
    fp=fopen(path_name, "r");
    g_assert( fp != NULL);
    fseek(fp, 0L, SEEK_END);
    file_size = ftell(fp);
    rewind(fp);
    g_debug("file size: %ld\n",file_size*sizeof(gchar));
    file_buffer=calloc(file_size, sizeof(gchar));
    g_assert(file_buffer != NULL);
    fread(&file_buffer,file_size,1,fp);
    g_debug("after fread");
    //file_buffer[file_size*sizeof(gchar)]=0;
    //g_debug("after adding zero: %s",file_buffer);
    gtk_text_buffer_set_text (textbuffer, file_buffer,2);
    g_debug("after set text");
    g_object_unref(file);
}

this is the output of my application:

** (tour_de_gtk:18107): DEBUG: /home/ufk/Projects/gtk-projects/tour-de-gtk/Debug/src/examples/example_gtk_label/main.c is chosen

** (tour_de_gtk:18107): DEBUG: file size: 16

** (tour_de_gtk:18107): DEBUG: after fread 

after then i get a segmentation fault on the command gtk_text_buffer_set_text

as you can see i have two commands that are commented out. trying to g_debug the buffer which obviously creates a segmentation fault because i didn't add a zero to the end of the string, and even when I try to add zero to the end of the string i get a segmentation fault. I probably did something wrong.

here i'm trying to write only the first two characters of the buffer but with no luck.

any ideas?

update

the finished function:

void on_file_activated(GtkWidget *widget, gpointer data) {
GFile *file;
gchar *path_name;
long file_size;
gchar *file_buffer;
GError *error;
gboolean read_file_status;
file = gtk_file_chooser_get_file(GTK_FILE_CHOOSER(widget));
path_name=g_file_get_path(file);
g_debug("%s is chosen\n", path_name);
read_file_status=g_file_get_contents (path_name,&file_buffer,NULL, &error);

if (read_file_status == FALSE) {
    g_error("error opening file: %s\n",error && error->message ? error->message : "No Detail");
    return;
}
gtk_text_buffer_set_text (textbuffer, file_buffer,-1);
g_debug("after set text");
g_object_unref(file);
}

Answer 1

There are a lot of improvements possible here, you may already know many and just be messing around, but I'll list several in case.

gchararray file_buffer;

Just use char*

g_assert( fp != NULL);

Should use assert for programming errors, not runtime errors, so here g_printerr() or a dialog would be better

fseek(fp, 0L, SEEK_END); file_size = ftell(fp); rewind(fp);

fstat(fileno(fp), &statbuf) is probably a better way to do this, but the whole approach is kind of bad; rather than get the size, it's better to just read into a dynamically-growing buffer. Or if you're willing to preallocate the whole buffer, just use g_file_get_contents(). Another approach is g_file_query_info() (which is more portable and uses the vfs)

file_buffer=calloc(file_size, sizeof(gchar));

g_new0(char, file_size) is nicer, or g_malloc0(file_size). Also you need file_size+1 to make room for the nul byte.

fread(&file_buffer,file_size,1,fp);

Here you want file_buffer (a char*) rather than &file_buffer (a char**). This is probably the actual cause of the immediate breakage.

You also need to check the return value of fread().

Also missing here is g_utf8_validate() on the data read in.

Have a look at the implementation of g_file_get_contents() to see one approach here. You could also use g_file_load_contents to use a GFile instead of a path (portable, uses vfs) or better yet in a real-world app, g_file_load_contents_async().

To debug segfaults, the two best tools are:

• run in gdb, wait for crash, then type "bt"; be sure to use -g with your compiler when you compile
• run in valgrind, see where it says you look at bad memory