How to overwrite an array of char pointers with a larger list of char pointers?
- by Casey
My function is being passed a struct containing, among other things, a NULL terminated array of pointers to words making up a command with arguments.
I'm performing a glob match on the list of arguments, to expand them into a full list of files, then I want to replace the passed argument array with the new expanded one.
The globbing is working fine, that is, g.gl_pathv is populated with the list of expected files. However, I am having trouble copying this array into the struct I was given.
#include <glob.h>
struct command {
char **argv;
// other fields...
}
void myFunction( struct command * cmd )
{
char **p = cmd->argv;
char* program = *p++; // save the program name (e.g 'ls', and increment to the first argument
glob_t g;
memset(&g, 0, sizeof(g));
g.gl_offs = 1;
int res = glob(*p++, GLOB_DOOFFS, NULL, &g);
glob_handle_res(res);
while (*p)
{
res = glob(*p, GLOB_DOOFFS | GLOB_APPEND, NULL, &g);
glob_handle_res(res);
}
if( g.gl_pathc <= 0 )
{
globfree(&g);
}
cmd->argv = malloc((g.gl_pathc + g.gl_offs) * sizeof *cmd->argv);
if (cmd->argv == NULL) { sys_fatal_error("pattern_expand: malloc failed\n");}
// copy over the arguments
size_t i = g.gl_offs;
for (; i < g.gl_pathc + g.gl_offs; ++i)
cmd->argv[i] = strdup(g.gl_pathv[i]);
// insert the original program name
cmd->argv[0] = strdup(program);
** cmd->argv[g.gl_pathc + g.gl_offs] = 0; **
globfree(&g);
}
void
command_free(struct esh_command * cmd)
{
char ** p = cmd->argv;
while (*p) {
free(*p++); // Segfaults here, was it already freed?
}
free(cmd->argv);
free(cmd);
}
Edit 1: Also, I realized I need to stick program back in there as cmd-argv[0]
Edit 2: Added call to calloc
Edit 3: Edit mem management with tips from Alok
Edit 4: More tips from alok
Edit 5: Almost working.. the app segfaults when freeing the command struct
Finally: Seems like I was missing the terminating NULL, so adding the line:
cmd->argv[g.gl_pathc + g.gl_offs] = 0;
seemed to make it work.
