Using strtok and get "cannot convert 'char*' to 'char**' in assignment" - c++

Question

I am trying to make a program that reads a string from a file in SPIFFS with 4 tab-separated things and then processes it into four char arrays to be used in another function. However, I get the error cannot convert 'char*' to 'char**' in assignment. Is there any idea why? Here's my code:
#include <string.h>
#include "FS.h"
#include "AdafruitIO_WiFi.h"
char *ssid;
char *pass;
char *aiduser;
char *aidkey;
// comment out the following two lines if you are using fona or ethernet
#include "AdafruitIO_WiFi.h"
//AdafruitIO_WiFi io(IO_USERNAME, IO_KEY, WIFI_SSID, WIFI_PASS);
void setupWifi(char* *aiduser, char* *aidkey, char* *ssid, char* *pass){
#define WIFIFILE "/config.txt"
int addr = 0;
bool spiffsActive = false;
if (SPIFFS.begin()) {
spiffsActive = true;
}
File f = SPIFFS.open(WIFIFILE, "r");
String str;
while (f.position()<f.size())
{
str=f.readStringUntil('\n');
str.trim();
}
// Length (with one extra character for the null terminator)
int str_len = str.length() + 1;
// Prepare the character array (the buffer)
char char_array[str_len];
// Copy it over
str.toCharArray(char_array, str_len);
const char s[2] = {9, 0};
/* get the first token */
aiduser = strtok(char_array, s);
aidpass = strtok(NULL, s);
ssid = strtok(NULL, s);
pass = strtok(NULL, s);
/* walk through other tokens
while( token != NULL ) {
printf( " %s\n", token );
token = strtok(NULL, s);
}*/
// RESULT: A thingy
}
void setup(){
setupWifi(&aiduser, &aidkey, &ssid, &pass);
AdafruitIO_WiFi io(aiduser, aidkey, ssid, pass);}
Also, I can't run the setupWifi function unless it is in setup or loop, but I can't make it in another setup because this is #included into another main file.

Answer 1

You get this error because of this:
void setupWifi(char* *aiduser, char* *aidkey, char* *ssid, char* *pass)
{
...
aiduser = strtok(char_array, s);
aidpass = strtok(NULL, s);
ssid = strtok(NULL, s);
pass = strtok(NULL, s);
}
This variables are double pointers, strtok returns a pointer to char, those
are not compatible types.
Because strtok returns char_array + some_offset and char_array is a local
variable in setupWifi, you need to do a copy for each of them and return the
copy instead. You can do it with strdup.
*aiduser = strdup(strtok(char_array, s));
*aidpass = strdup(strtok(NULL, s));
*ssid = strdup(strtok(NULL, s));
*pass = strdup(strtok(NULL, s));
I encourage you to always check the return value of strdup, because it can
return NULL.1
If your system does not have strdup, then you can write your own:
char *strdup(const char *text)
{
if(text == NULL)
return NULL;
char *copy = calloc(strlen(text) + 1, 1);
if(copy == NULL)
return NULL;
return strcpy(copy, text);
}
One last thing:
void setupWifi(char* *aiduser, char* *aidkey, char* *ssid, char* *pass);
It looks really awkward, never seen declaring double pointer this way. Much
easier to read would be
void setupWifi(char **aiduser, char **aidkey, char **ssid, char **pass);
Fotenotes
1While the syntax is correct, I still consider this bad practice,
because you should always check the return values of functions that return
pointers. If they return NULL, you cannot access the memory. This adds a
little bit of more code, but your program will not die of segfaults and it can
recover from the errors.
I'd also change your function to return 1 on success, 0 otherwise:
int parse_and_set(char *txt, const char *delim, char **var)
{
if(delim == NULL || var == NULL)
return 0;
char *token = strtok(txt, delim);
if(token == NULL)
return 0;
token = strdup(token);
if(token == NULL)
return NULL;
*var = token;
return 1;
}
void init_parse(char ***vars, size_t len)
{
for(size_t i = 0; i < len; ++i)
**(vars + i) = NULL;
}
int cleanup_parse(char ***vars, size_t len, int retval)
{
for(size_t i = 0; i < len; ++i)
{
free(**(vars + i));
**(vars + i) = NULL;
}
}
int setupWifi(char **aiduser, char **aidkey, char **ssid, char **pass)
{
if(aiduser == NULL || aidkey == NULL || ssid == NULL || pass == NULL)
return 0;
...
/* get the token token */
char **vars[] = { aiduser, aidkey, ssid, pass };
size_t len = sizeof vars / sizeof *vars;
init_parse(vars, len);
if(parse_and_set(char_array, s, aiduser) == 0)
return cleanup_parse(vars, len, 0);
if(parse_and_set(NULL, s, aidpass) == 0)
return cleanup_parse(vars, len, 0);
if(parse_and_set(NULL, s, ssid) == 0)
return cleanup_parse(vars, len, 0);
if(parse_and_set(NULL, s, pass) == 0)
return cleanup_parse(vars, len, 0);
...
return 1;
}