c - String manipulation code using char ** pointer gives unexpected result -

i trying implement string parsing code need substring of given string deed following:

the header file : test.h

#ifndef header_file #define header_file  #include<stdio.h> #include<string.h>   int increment(char **);  #endif   

the source files : main.c test.c

test.c :

1. case1 :test.c

   #include"test.h"

   int increment(char **string){

       char *temp = *(string);     int value;       if(temp != null){              *(string) = ++temp;             value = 1;     }      else{             value = 0;     }      return value; 

   }

2. case2 :test.c

   #include"test.h"

   int increment(char **string){

       char *temp = *(string);     int value;       if(*temp != '\0'){              *(string) = ++temp;             value = 1;     }      else{             value = 0;     }      return value; 

   }

main.c:

#include"test.h"  int main() {         char str[30] = "i have done form here comes.";         char strs[50];          char *p = str;          memset(strs, 0, 50);          while(increment(&p))         {                 strcpy(strs,p);                 printf("originally string : %s\n", str);                 printf("the modified string   : %s\n", strs);                 memset(strs, 0, 50);         }          return 0; } 

the makefile :

#this makefile.  : run main.o test.o  run : main.o test.o         $(cc) -g $^ -o $@  %.o : %.c         $(cc) -g -c $^ -o $@  .phony : clean  clean :          -rm -f *.o run 

but in first case in test.c tried traversed sub-string giving garbage result. , second case works fine.

what going wrong in test.c case 1.

thanks!!!!!!!!!!!!

the purpose add prefix , suffix every word in string need string before word , word , , after word. ex: prefix_i_suffix have done form here comes. prefix_have_suffix have done form here comes.

you're doing few things wrong.

1. i don't see splitting words spaces anywhere @ all, , seems main requirement.
2. i see, however, insane operations on pointers. frankly, can't understand logic behind them.

so let me give examples how can done - without modifying pointers @ all:

#include <stdio.h> #include <string.h>  int main () {     char str[] = "i have done answer here comes.";      const char *delimiters = " ";     char *pch = strtok(str, delimiters);     while (pch != null)     {         printf("prefix_%s_suffix\n", pch);         pch = strtok(null, delimiters);     }     return 0; } 

with copying input intermediate array can modify want:

#include <stdio.h> #include <stdlib.h> #include <string.h>  int main () {     char str[] = "i have done answer here comes.";      char **array = null;     size_t array_size = 0;      const char *delimiters = " ";     char *pch = strtok(str, delimiters);     while (pch != null)     {         size_t str_size = strlen(pch) + 1; //to accommodate `\0` byte         char *str_copy = malloc(str_size);         if (!str_copy)         {             printf("no memory!");             return 1;         }         memcpy(str_copy, pch, str_size);          ++ array_size;         array = realloc(array, sizeof(char*) * array_size);         if (!array)         {             printf("no memory!");             return 1;         }         array[array_size - 1] = str_copy;          pch = strtok(null, delimiters);     }      (size_t = 0; < array_size; ++)     {         printf("prefix_%s_suffix\n", array[i]);         free(array[i]);     }     free(array);      return 0; }