Segmentation fault - splitting command into tokens - c

Question

The code I am implementing in which I split the command first by pipes then by spaces.
int main(){
pid_t pid;
while (1) {
printf("$ ");
char *cmd;
ssize_t size=0;
getline(&cmd,&size,stdin);
if (cmd[strlen(cmd)-1]== '\n') {cmd[strlen(cmd)-1]='\0';}
char** commands = splitter(cmd,"|");
int i=0;
int fd[2],in=0;
while (commands[i+1]!=NULL){
pipe(fd);
char **args = splitter(commands[i]," \t");
pid = fork();
if (pid==-1) {exit(EXIT_FAILURE);}
else if (pid==0){
close(fd[0]);
changeIO(in,0);
changeIO(fd[1],1);
execvp(args[0],args);
}
else{
waitpid(pid,NULL,0);
close(fd[1]);
close(in);
in = fd[0];
}
i++;
}
char **args = splitter(commands[i+1]," \t");
changeIO(in,0);
execvp(args[0],args);
}
}
Here follows the implementation of the functions the code above uses
void changeIO(int oldfd,int newfd){
if (oldfd!=newfd){
dup2(oldfd,newfd);
close(oldfd);
}
}
char** splitter(char* stringToSplit, char* delimiter){
char *token;
int initial_size = 300;
char** args = malloc(initial_size*sizeof(char*));
token = strtok(stringToSplit,delimiter);
int index = 0;
while (token != NULL) {
args[index] = token;
index++;
if (index >= initial_size) {
initial_size = initial_size + 100;
args = realloc(args,initial_size*sizeof(char*));
if (!args) exit(EXIT_FAILURE);
}
token = strtok(NULL,delimiter);
}
args[index] = NULL;
return args;
}
Ok executing the code I get a segmentation fault when I enter the command in the user input. Testing various options I came to realize it has something to do with the char** args in which I pass the tokens of each commands. I can't understand why this happens since memory is allocated and from what I understand I just point the pointer args to that allocated memory. Any help appreciated.
EDIT: Checked with valgrind. Results below:
==3361== Memcheck, a memory error detector
==3361== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==3361== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==3361== Command: ./mysh3
==3361==
==3361== Conditional jump or move depends on uninitialised value(s)
==3361== at 0x40AFE97: getdelim (iogetdelim.c:59)
==3361== by 0x40ACDD1: getline (getline.c:32)
==3361== by 0x80486C4: main (in /home/dimitris/Desktop/mysh3)
==3361==
$ ls
==3361== Invalid read of size 1
==3361== at 0x4101CAA: execvpe (execvpe.c:50)
==3361== by 0x4101B33: execvp (execvp.c:26)
==3361== by 0x804885F: main (in /home/dimitris/Desktop/mysh3)
==3361== Address 0x0 is not stack'd, malloc'd or (recently) free'd
==3361==
==3361==
==3361== Process terminating with default action of signal 11 (SIGSEGV)
==3361== Access not within mapped region at address 0x0
==3361== at 0x4101CAA: execvpe (execvpe.c:50)
==3361== by 0x4101B33: execvp (execvp.c:26)
==3361== by 0x804885F: main (in /home/dimitris/Desktop/mysh3)
==3361== If you believe this happened as a result of a stack
==3361== overflow in your program's main thread (unlikely but
==3361== possible), you can try to increase the size of the
==3361== main thread stack using the --main-stacksize= flag.
==3361== The main thread stack size used in this run was 8388608.
==3361==
==3361== HEAP SUMMARY:
==3361== in use at exit: 2,520 bytes in 3 blocks
==3361== total heap usage: 5 allocs, 2 frees, 4,568 bytes allocated
==3361==
==3361== LEAK SUMMARY:
==3361== definitely lost: 0 bytes in 0 blocks
==3361== indirectly lost: 0 bytes in 0 blocks
==3361== possibly lost: 0 bytes in 0 blocks
==3361== still reachable: 2,520 bytes in 3 blocks
==3361== suppressed: 0 bytes in 0 blocks
==3361== Rerun with --leak-check=full to see details of leaked memory
==3361==
==3361== For counts of detected and suppressed errors, rerun with: -v
==3361== Use --track-origins=yes to see where uninitialised values come from
==3361== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
Segmentation fault

Answer 1

It's an off-by-one array index.
Your while loop finishes with commands[i+1] being null. Then you pass it to splitter.
Pass commands[i] instead.

Answer 2

When strtok() finds a token, it changes the character immediately after the token into a \0, and then returns a pointer to the token.