split strings with strtok and then save them error - c

Question

i Have the following code
char inputs []="3,0,23.30,3,30/55,55,55,55,55,55,55,55,55,55,55,55,55,64,64,64,100,100,100,100,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,55,55,70/1.5,0.5,0.2,0.2,0.3,0.1";
char parameters[18];
strcpy(parameters,strtok(inputs,"/"));
and then some code to transmit my characters through uart and see them at a monitor. when i transmit the inputs i see them fine but when i transmit the parameters i see nothing the string is empty.
i have seen examples for strtok and it uses that code to split strings. I have also tried this kind of code at visual studio and when i print them it shows me the strings fine. Is there any chance that strtok doesn't function well with a microprocessor????

Answer 1

While working with microcontrollers, you have to take care from which memory area you are working on. On software running on a PC, everything is stored and run from the RAM. But, on a flash microcontroller, code is run from flash (also called program memory) while data are processed from RAM (also called data memory).
In the case you are working on, the inputs variable is storing an hardcoded character array, which can be const, and we don't know in which area the compiler chose to put it. So, we could rewrite you small program just to make sure that all the data are stored in program data and we will use the "_P" functions to manipulate this data.
#include <avr/pgmspace.h > // to play in program space
const char inputs PROGMEM []="3,0,23.30,3,30/55,55,55,55,55,55,55,55,55,55,55,55,55,64,64,64,100,100,100,100,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,55,55,70/1.5,0.5,0.2,0.2,0.3,0.1"; // Now, we are sure this is in program memory space
char buffer[200]; // should be long enough to contain a copy of inputs
char parameters[18];
int length = strlen_P(inputs); // Should contains string length of 186 (just to debug)
strcpy_P(buffer,inputs); // Copy the PROGMEM data in data memory space
strcpy(parameters,strtok_P(buffer,"/")); // Parse the data now in data memory space
For more info on program space with avr gcc : http://www.nongnu.org/avr-libc/user-manual/pgmspace.html

Answer 2

I don't use strtok much, if at all, but this appears to be the correct way to store the result of strtok() in an char[]:
const int NUM_PARAMS = 18;
const int MAX_CHARS = 64;
char parameters[NUM_PARAMS][MAX_CHARS];
char delims[] = "/";
char *result = NULL;
int count = 0;
result = strtok(inputs, delims);
while(result != NULL && count < NUM_PARAMS){
strncpy(parameters[count++], result, MAX_CHARS);
result = strtok(NULL, delims);
}
or this if you don't want to allocate unnecessary memory for smaller tokens:
const int NUM_PARAMS = 18;
char* parameters[NUM_PARAMS];
char delims[] = "/";
char *result = NULL;
int count = 0;
result = strtok(inputs, delims);
while(result != NULL && count < NUM_PARAMS){
parameters[count] = malloc(strlen(result) + 1);
strncpy(parameters[count++], result, MAX_CHARS);
result = strtok(NULL, delims);
}
parameters should now contain all of your tokens.

Answer 3

strtok() intentionally modifies the source string, replacing tokens with terminators as it goes. There is no reason to store the content in auxiliary storage whatsoever so long as the source string is mutable.
Splitting the string into conjoined constants (which will be assembled by the compiler, so they ultimately will be a single terminated string):
char inputs []="3,0,23.30,3,30/"
"55,55,55,55,55,55,55,55,55,55,55,55,55,64,64,64,100,100,100,100,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,55,55,70/"
"1.5,0.5,0.2,0.2,0.3,0.1";
Clearly the second and third sequences delimited by '/' are nowhere near 17 chars wide (remember, your copy needs one more place for the terminator, thus only 17 chars can legally be copied).
Unless there is a compelling reason to do otherwise, I see no reason you can't simply do this:
char *param = strtok(inputs, "/");
while (param != NULL)
{
// TODO: do something with param...
// ... then advance to next param
param = strtok(NULL, "/");
}
What you do with // TODO do something with param... is up to you. The length of the parameter can be retrieved by strlen(param), for example. You can make a copy, providing you have enough storage space as the destination (in the second and third cases, you don't provide enough storage with only an 18-char buffer in your example).
Regardless, remember, strtok() modifies the source inputs[] array. If that is not acceptable an alternative would be something like:
char *tmp_inputs = strdup(inputs);
if (tmp_inputs != NULL)
{
char *param = strtok(tmp_inputs, "/");
while (param != NULL)
{
// TODO: do something with param...
// ... then advance to next param
param = strtok(NULL, "/");
}
// done with copy of inputs. free it.
free(tmp_inputs);
}
There are considerably threading decisions to make as well, the very reason the version of strtok() that requires the caller (you) to tote around context between calls was invented. See strtok_r() for more information.

Answer 4

You have to initialialize parameters that way :
char parameters[18] = {'\0'};
Thus, it will be initialized with null characters instead of variable values. This is important, because strcpy will try to find a null character to identify the end of the string.
Just to make it clear...
parameters after its initialisation : [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
parameters after strtok : ['3',',','0',',','2','3','.','3','0',',','3',',','3','0',0,0,0,0]