outsourcing strtok() in function in c -

i want outsource string operation function , ask results in main. doesn't work, , don't understand why.

#include <stdio.h> #include <string.h>  void splitrequest(char request[], char method[], char ressource[], char proto[]) {      method = strtok(request, " ");     ressource = strtok(null, " ");     proto = strtok(null, " ");     printf("\nresult:\n\nmethod:\t\t%s\nressource:\t%s\nproto:\t\t%s\n",method,ressource,proto); }  int main() {         char method[50], ressource[50], proto[50], request[50];     memset(method, '\0', 50);     memset(ressource, '\0', 50);     memset(proto, '\0', 50);     memset(request, '\0', 50);     strcpy(request,"get /index.htm http/1.1");      //rehash query     splitrequest(request, method, ressource, proto);      //check results     printf("\nresult:\n\nmethod:\t\t%s\nressource:\t%s\nproto:\t\t%s\n",method,ressource,proto);      return 0; } 

in splitrequest function arguments pointers. , more importantly local variables. changes them (like making them point anywhere else) affect local variable, nothing else.

the solution copy memory instead. perhaps like

char *temp;  if ((temp = strtok(request, " ")) != null) {     strcpy(method, temp); }  // , on... 

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a little elaboration mean...

in c function arguments passed by value. means value copied , function have local copy of value. chaning copy of course not change original value.

it same pointers. when call splitrequest function pointers pass copied. inside function variable method (for example) pointing memory of array defined in main function. when assign variable, with

method = strtok(...); 

you modify local variable, local copy of pointer. when function returns local variable method goes out of scope, , changes lost.

there 2 solutions problem. 1 emulate pass reference (something c doesn't have, why must emulated), not work long have array. therefore second , easiest solution: copy memory pointed local variable method, show above.

an important note though: when call splitrequest function, passing arrays, arrays not passed. instead arrays decays pointer first element, , inside function variables defined arguments pointers , not arrays.

the call

splitrequest(request, method, ressource, proto); 

is equal to

splitrequest(&request[0], &method[0], &ressource[0], &proto[0]); 

and function declaration

void splitrequest(char request[], char method[], char ressource[], char proto[]) 

is equal to

void splitrequest(char *request, char *method, char *ressource, char *proto) 

so no strings not copied, pointers. otherwise have gotten error when assigning pointer, since can't assign arrays copy them.