Segmentation fault using fgets in C - c

Question

My code is not working and it is when I call fgets in the commandSplit function. I figured this out by printing "Am I here" in multiple places and find that the error at fgets it seems. I may be wrong, but I am pretty sure. I get a segmentation fault and I can not figure out why. Below is my code.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#define MAX_CHARACTERS 512
int Execute(char *a[], int t[], int num) {
int exitShell = 0;
int l = 0;
for (int i = 0; i < num; i++) {
int status;
if (strcmp(a[0], "quit") == 0) {
exitShell = 1;
}
if (t[i] && ((strcmp(a[l], "quit") == 0))) {
exitShell = 1;
}
char *holder[t[i]+1];
for (int j = 0; j < t[i]; j++) {
holder[j] = a[l];
l++;
}
holder[t[i]] = NULL;
pid_t p = fork();
pid_t waiting;
if (p == 0) {
execvp(holder[0], holder);
fprintf(stderr, "Child process could not execvp!\n");
exit(1);
} else {
if (p < 0) {
fprintf(stderr, "Fork FAILED!\n");
} else {
waiting = wait(&status);
printf("Child %d exit with status %d\n", waiting, status);
}
}
for (int g = 0; g < t[i]; g++) {
a[g] = NULL;
}
}
for (int i = 0; i < num; i++) {
t[i] = 0;
}
return exitShell;
}
int commandSplit(char *c, FILE *f, char *a[], int t[]) {
int count = 0;
int emptyfile = 1;
int stat = 0;
int total1 = 0;
char *temp[MAX_CHARACTERS];
if (c != NULL) {
char *readCommands = strtok(c, ";");
while (readCommands != NULL) {
temp[count] = readCommands;
count++;
readCommands = strtok(NULL, ";");
}
for (int i = 0; i < count; i++) {
char *read = strtok(temp[i], " ");
int track1 = 0;
while (read != NULL) {
a[total1] = read;
track1++;
total1++;
read = strtok(NULL, " ");
}
t[i] = track1;
}
stat = Execute(a, t, count);
} else {
char *buildCommands = "";
printf("Am I here???\n");
while ((fgets(buildCommands, MAX_CHARACTERS, f) != NULL) && !stat) {
printf("Am I here???\n");
emptyfile = 0;
commandSplit(buildCommands, NULL, a, t);
stat = Execute(a, t, count);
}
if (emptyfile) {
printf("File is empty!\n");
stat = 1;
}
}
printf("Am I here???\n");
return stat;
}
int main(int argc, char *argv[]) {
int exitProgram = 0;
FILE *fileRead = NULL;
if (argc == 2) {
fileRead = fopen(argv[1], "r");
if (fileRead == NULL) {
printf("No such file exists\n");
exitProgram = 1;
}
}
if (argc > 2) {
printf("Incorrect batch mode call\n");
exitProgram = 1;
}
char *args[MAX_CHARACTERS];
int tracker[MAX_CHARACTERS];
while (!exitProgram) {
if (argc == 1) {
char *commands = (char *)(malloc(MAX_CHARACTERS * sizeof(char)));
printf("tinyshell>");
if (fgets(commands, MAX_CHARACTERS, stdin) == NULL) {
exitProgram = 1;
printf("\n");
}
int len;
len = strlen(commands);
if (len > 0 && commands[len-1] == '\n') {
commands[len-1] = '\0';
}
if (len > MAX_CHARACTERS) {
printf("TOO MANY CHARACTERS - MAX: 512\n");
continue;
}
if (strlen(commands) == 0)
continue;
exitProgram = commandSplit(commands, NULL, args, tracker);
} else {
exitProgram = commandSplit(NULL, fileRead, args, tracker);
}
}
fclose(fileRead);
return 0;
}

Answer 1

As commented #Jean-François Fabre , buildCommands points to insufficient space and potential const space;
char *buildCommands = "";
...
// bad code
while ((fgets(buildCommands, MAX_CHARACTERS, f) != NULL) && !stat) {
Allocate space with an array or malloc()
char buildCommands[MAX_CHARACTERS];
...
while ((fgets(buildCommands, sizeof buildCommands, f) != NULL) && !stat) {
...
}
// or
char *buildCommands = malloc(MAX_CHARACTERS);
assert(buildCommands);
...
while ((fgets(buildCommands, MAX_CHARACTERS, f) != NULL) && !stat) {
...
}
...
free(buildCommands);