Unable to run ./program with exec and makeargv in c - c

Question

So to start off, this program has two main parts. The first takes input from the command line using fgets and then makes an argv array with a function called makeargv. The second, takes that argv array and runs it using execvp. The problem I am having is that the program will only run system programs such as "ls", "pwd", "vim", etc. but will not run any program when the directory is specified, such as "./program". I have already tried different versions of exec but the only difference that has made is that then my program will no longer run any commands.
For the below program I cut out all the code that was not relevant to the question to avoid confusion.
#ifndef MAX_CANON
#define MAX_CANON 8192
#endif
int makeargv(const char *s, const char *delimiters, char ***argvp);
int main (int argc, char *argv[]) {
char cmd[MAX_CANON];
char delim[] = "\t";
char **myargv;
printf("Beginning program...\nEnter a command to execute:\n");
while(fgets(cmd, MAX_CANON, stdin) != NULL){ // Here's where I get input from the command line
/* Remove newline from end of command */
if (*(cmd + strlen(cmd) - 1) == '\n' || *(cmd + strlen(cmd) - 1) == ' ' )
*(cmd + strlen(cmd) - 1) = 0;
/*---- Child Code ----*/
if((p = fork()) == 0){
if (makeargv(cmd, delim, &myargv) == -1) { // Here is where I make the argv array
fprintf(stderr, "Child failed to construct an argument array for %s\n", &cmd[0]);
return 1;
}
fprintf(stderr, "Command is: %s\n", *&myargv[0]);
if(execvp(myargv[0], &myargv[0]) == -1){ // Here is where the error keeps appearing
fprintf(stderr, "Error: Failed to execute command!\n");
return 1;
}
return 0;
}
/*---- Parent Code ----*/
Here is the makeargv code
#include <errno.h>
#include <stdlib.h>
#include <string.h>
int makeargv(const char *s, const char *delimiters, char ***argvp) {
int error;
int i;
int numtokens;
const char *snew;
char *t;
if ((s == NULL) || (delimiters == NULL) || (argvp == NULL)) {
errno = EINVAL;
return -1;
}
*argvp = NULL;
snew = s + strspn(s, delimiters); /* snew is real start of string */
if ((t = malloc(strlen(snew) + 1)) == NULL)
return -1;
strcpy(t, snew);
numtokens = 0;
if (strtok(t, delimiters) != NULL) /* count the number of tokens in s */
for (numtokens = 1; strtok(NULL, delimiters) != NULL; numtokens++) ;
/* create argument array for ptrs to the tokens */
if ((*argvp = malloc((numtokens + 1)*sizeof(char *))) == NULL) {
error = errno;
free(t);
errno = error;
return -1;
}
/* insert pointers to tokens into the argument array */
if (numtokens == 0)
free(t);
else {
strcpy(t, snew);
**argvp = strtok(t, delimiters);
for (i = 1; i < numtokens; i++)
*((*argvp) + i) = strtok(NULL, delimiters);
}
*((*argvp) + numtokens) = NULL; /* put in final NULL pointer */
return numtokens;
}
Edit:
Swapped fprintf for perror.
if(execvp(myargv[0], &myargv[0]) == -1){ // Here is where the error keeps appearing
fprintf(stderr, "Error: Failed to execute command!\n");
return 1;
}
if(execvp(myargv[0], &myargv[0]) == -1){ // Here is where the error keeps appearing
perror("Error: Failed to execute command!\n");
return 1;
}
I am now getting a "No such file or directory" error.
FIXED:
The makeargv program was using "\t" as it's delimeter instead of " " so it was not creating the array correctly.
Changing:
char delim[] = "\t";
To:
char delim[] = " ";
Fixes the problem.

Answer 1

There is 2 type of exec:
the first need a path as the environment PATH who contain a location (where find sys executables)
and the others how take real file location.
Form the man page (https://linux.die.net/man/3/exec):
The execlp(), execvp(), and execvpe() functions duplicate the actions of the shell in searching for an executable file if the specified filename does not contain a slash (/) character.
So this mean that you need to use an absolute location, who always begin with /.
You can use getwd() and strcat() to concatenate the 2 strings.
For execvp:
int execvp(const char *file, char *const argv[]); // From the man (I <3 mans)
So:
char argv[3][] = { "/bin/ls", "/", NULL};
if (execvp("/bin/ls", argv) == -1)
return (1);
For evecv:
int execv(const char *path, char *const argv[]);
There is a problem, it need the system PATH. If you don't know what it is type "echo $PATH" in bash. It's a list of directories where the system can find binaries like "ls" in "/bin", concatenate with ":" as sparator. I find the exact definition here.
For your makeargv:
I don't understand why you deference it and take the address after.
execvp(myargv[0], &myargv[0])
char **myargv; //That's we have
char *const argv[]; //that's we need
//so you should try simply:
execvp(myargv[0], myargv);
//or if there is a cast problem
execvp(myargv[0], (char *const[])myargv);
Good luck!