Thread: Strings and tokenizing need help

hi all i am new to the programing world & specially C with no sources of help available

i hope someone here would help

i am writing a simple code to extract words from a string & printing it

i have spent a lot of time trying to do so, yet i still have problems

not to waist ur time this is the program requirement i am suppose to do


start programming by developing and testing a simple C function. Specifically, write the function
void getCmd (int *argc, char *argv[])

which reads a command line from the standard input device (keyboard) and returns the
number of words/tokens in that command line in the integer variable argc and pointers
to the individual words/tokens in the character vector argv[]. Thus, argc should
contain the number of strings in the command line (the program name and the
arguments) and the array of character strings argv contains each of these strings —
pointer to the program name in argv[0], pointer to the first parameter in argv[1],
pointer to the second parameter in argv[2], etc. You should identify the words/tokens
in a command line by searching for the space character(s) delimiting the words/tokens.
In particular, you should not use any library function to extract the words/tokens in a
character string.
In order to systematically develop your program, first write the algorithm to perform
the above in pseudo code form. Be sure to show the words in a command line are
identified and how argc and argv[] are computed. Then implement your algorithm as
the C function getCmd.

Write a main program (and store it in the file getCmd.c) which calls your getCmd
function to read a command line and print the command line, the value of argc and the
words in the command line as shown below. For example, for the command line
copy ~/Pract1/getCmd.c ~/Pract2/getCmd.c
the output of your main program should be
The command line ‘copy ~/Pract1/getCmd.c ~/Pract2/getCmd.c’ contains the following 3 words:
copy, ~/Pract1/getCmd.c, ~/Pract2/getCmd.c

Test your program with at least the following command lines.
cd ~/Pract2
copy ~/Pract/getCmd.c ~/Pract/getCmd.c
copy copy
cp getCmd.c getCmd.c
del copy
del getCmd.c
ren copy copy.test
ren getCmd.c getCmd.c


This is the code i wrote so far it is a bit stupid but this is really my first shot @ C
and what makes it worse is that i am not suppose to use any of the special library functions ;(.

Code:

#include <stdio.h>

void getCmd (int *argc, char **argv[]){
  int endv;
  char pos[7];
  int p;
  int tokens;
  p=0;

for (int l=0; *argv[l] != '\r';l++){
  if ( argv[l]=='\0'){
    p=p+1;
    pos[p]=l;
    tokens= tokens+1;
   
  }
 }

endv = l;
argc = tokens;
  int loc;
  loc=0;     
    (*argc) = 0;

    argv[(*argc)++] = userInput+(pos[loc]);

loc++;
    argv[(*argc)++] = userInput+(pos[loc]);

loc++;
    argv[(*argc)++] = userInput+(pos[loc]);
}
int main(){

    char userInput[256];
    
    printf("type a string:  ");
    fgets(userInput, 256, stdin);
    printf("The command line ' %s ' contains the following ", userInput);

    int i;
    int cmdc;
    char* cmdv[20];

    getCmd(&cmdc, cmdv);
    for(i=0;i<cmdc; i++){
	printf("argument %d is %s\n", i, cmdv[i]);    
    }
    return 0;

}

i have updated the code and the program compiles but when i run it and type the values it gives me an error Segmentation fault (core dumped)

Code:

#include <stdio.h>

   char userInput[256];
void getCmd (int *argc, char *argv[]){
  int endv;
  char pos[7];
  int p;
  int l;
  int tokens;
  p=0;

for ( l=0;*argv[l]!='\r';l++){
  if ( *argv[l]=='\0'){
    p=p+1;
    pos[p]=l;
    tokens= tokens+1;
   
  }
 }

endv = l;
*argc = tokens;
  int loc;
  loc=0;     
    (*argc) = 0;

    argv[(*argc)++] = userInput+(pos[loc]);

    loc = loc+1;
    argv[(*argc)++] = userInput+(pos[loc]);

loc++;
    argv[(*argc)++] = userInput+(pos[loc]);
}

int main(){
    
    printf("type a string:  ");
    fgets(userInput, 256, stdin);
    printf("The command line ' &#37;s ' contains the following ", userInput);

    int i;
    int cmdc;
    char* cmdv[20];

    getCmd(&cmdc, cmdv);
    for(i=0;i<cmdc; i++){
	printf("argument %d is %s\n", i, cmdv[i]);    
    }
    return 0;

}

ok so i am now a bit confused
the array or string userInput is used to in the function "fgets" to store the users input

now i am trying to pass the array to the getCmd function to have it tokenizing the string i was pass en an empty one if i understood your reply correctly but when i try to pas the userInput array

still geting the "Segmentation fault (core dumped)"

Code:

#include <stdio.h>

//   char userInput[256];
char *userInput;
   int tokens;
   int endv;
   char pos[7];
   int p;
   int m;

void getCmd (int *argc, char* argv[]){

*argc = tokens;

  int loc;
  loc=0;     
    (*argc) = 0;

    argv[(*argc)++] = userInput+(pos[loc]);
    loc++;
    userInput[(pos[loc])] = '\0';

    argv[(*argc)++] = userInput+((pos[loc])+1);
    loc++;

    userInput[(pos[loc])] = '\0';
    argv[(*argc)++] = userInput+((pos[loc])+1);
}

int main(){
    
    printf("type a string:  ");
    //    fgets(userInput, 256, stdin);
    fgets(userInput, 265, stdin);

  p=0;
  // this is used to find the 
  for ( m=0;userInput[m]!='\0' ;m++){
  if ( userInput[m]==' '){
    p++;
    pos[p]=m;
    tokens++;
   
  }
 }
    endv = m;
    int i;
    int cmdc;
    char* cmdv[20];

    getCmd(&cmdc, cmdv);

    int firstturn = 0;
    for(i=0;i<cmdc; i++){

      if( firstturn=0){
	printf("The command line ' &#37;s ' contains the following %d words: ", userInput, tokens);
	    firstturn++;
      }
      printf("'%s, ", userInput[i]);
    }
    return 0;

}

i am almost giving up on it
i dont know whats the reason from this exersize
if the library functions are there why not use them
the only guess i have is that they want to split it for only the spaces
ohhhhh i am getting a big headache

Todd thanks for passing by,

i am 0 level beginner
i tried playing around with the debugger i guess i bugged the hell out of it yet i don't have a lot of knowledge about it to use it effectively.
i thought my mistake was obvious but the problem was with me, cause the requirements dont sound that impossible.