Help with malloc and free: Glibc detected: free(): invalid pointer
- by nunos
I need help with debugging this piece of code. I know the problem is in malloc and free but can't find exactly where, why and how to fix it. Please don't answer: "Use gdb" and that's it. I would use gdb to debug it, but I still don't know much about it and am still learning it, and would like to have, in the meanwhile, another solution.
Thanks.
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <sys/types.h>
#define MAX_COMMAND_LENGTH 256
#define MAX_ARGS_NUMBER 128
#define MAX_HISTORY_NUMBER 100
#define PROMPT ">>> "
int num_elems;
typedef enum {false, true} bool;
typedef struct {
char **arg;
char *infile;
char *outfile;
int background;
} Command_Info;
int parse_cmd(char *cmd_line, Command_Info *cmd_info)
{
char *arg;
char *args[MAX_ARGS_NUMBER];
int i = 0;
arg = strtok(cmd_line, " ");
while (arg != NULL) {
args[i] = arg;
arg = strtok(NULL, " ");
i++;
}
num_elems = i;precisa em free_mem
if (num_elems == 0)
return 0;
cmd_info->arg = (char **) ( malloc(num_elems * sizeof(char *)) );
cmd_info->infile = NULL;
cmd_info->outfile = NULL;
cmd_info->background = 0;
bool b_infile = false;
bool b_outfile = false;
int iarg = 0;
for (i = 0; i < num_elems; i++)
{
if ( !strcmp(args[i], "<") )
{
if ( b_infile || i == num_elems-1 || !strcmp(args[i+1], "<") || !strcmp(args[i+1], ">") || !strcmp(args[i+1], "&") )
return -1;
i++;
cmd_info->infile = malloc(strlen(args[i]) * sizeof(char));
strcpy(cmd_info->infile, args[i]);
b_infile = true;
}
else if (!strcmp(args[i], ">"))
{
if ( b_outfile || i == num_elems-1 || !strcmp(args[i+1], ">") || !strcmp(args[i+1], "<") || !strcmp(args[i+1], "&") )
return -1;
i++;
cmd_info->outfile = malloc(strlen(args[i]) * sizeof(char));
strcpy(cmd_info->outfile, args[i]);
b_outfile = true;
}
else if (!strcmp(args[i], "&"))
{
if ( i == 0 || i != num_elems-1 || cmd_info->background )
return -1;
cmd_info->background = true;
}
else
{
cmd_info->arg[iarg] = malloc(strlen(args[i]) * sizeof(char));
strcpy(cmd_info->arg[iarg], args[i]);
iarg++;
}
}
cmd_info->arg[iarg] = NULL;
return 0;
}
void print_cmd(Command_Info *cmd_info)
{
int i;
for (i = 0; cmd_info->arg[i] != NULL; i++)
printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]);
printf("arg[%d]=\"%s\"\n", i, cmd_info->arg[i]);
printf("infile=\"%s\"\n", cmd_info->infile);
printf("outfile=\"%s\"\n", cmd_info->outfile);
printf("background=\"%d\"\n", cmd_info->background);
}
void get_cmd(char* str)
{
fgets(str, MAX_COMMAND_LENGTH, stdin);
str[strlen(str)-1] = '\0';
}
pid_t exec_simple(Command_Info *cmd_info)
{
pid_t pid = fork();
if (pid < 0)
{
perror("Fork Error");
return -1;
}
if (pid == 0)
{
if ( (execvp(cmd_info->arg[0], cmd_info->arg)) == -1)
{
perror(cmd_info->arg[0]);
exit(1);
}
}
return pid;
}
void type_prompt(void)
{
printf("%s", PROMPT);
}
void syntax_error(void)
{
printf("msh syntax error\n");
}
void free_mem(Command_Info *cmd_info)
{
int i;
for (i = 0; cmd_info->arg[i] != NULL; i++)
free(cmd_info->arg[i]);
free(cmd_info->arg);
free(cmd_info->infile);
free(cmd_info->outfile);
}
int main(int argc, char* argv[])
{
char cmd_line[MAX_COMMAND_LENGTH];
Command_Info cmd_info;
//char* history[MAX_HISTORY_NUMBER];
while (true)
{
type_prompt();
get_cmd(cmd_line);
if ( parse_cmd(cmd_line, &cmd_info) == -1)
{
syntax_error();
continue;
}
if (!strcmp(cmd_line, ""))
continue;
if (!strcmp(cmd_info.arg[0], "exit"))
exit(0);
pid_t pid = exec_simple(&cmd_info);
waitpid(pid, NULL, 0);
free_mem(&cmd_info);
}
return 0;
}
