C Recursion (explain) Post: 302416390

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Top Forums Programming C Recursion (explain) Post 302416390 by jim mcnamara on Monday 26th of April 2010 10:29:59 AM

04-26-2010

Registered User

Code:

void printit(char line_of_char[], int index)
{
 if(line_of_char[index])
 {
  index++;
  printf("+%c", line_of_char[index]); /*how come this is not being printed after "-" was printed*/
  printit(line_of_char, index);
  printf("-%c", line_of_char[index]);
 }
}

function call pushes data onto the stack, so what this does is to push various
values of index onto the stack. The first print statement is using the value of index as it gets incremented 1,2,3 ...

The second printf (after the recursive call) statement is going "back in time" by popping values off the stack 10,9,8, .....

Change the code so it just prints value of the index variable, nothing else. Then you will see.

BTW the "if(line_of_char[index])" has a problem, the initial value is -1, which is the character before the start of the variable line_of_char. Apparently it works for you, but that it called "programming by coincidence" a really bad thing. It could trigger a segfault on other systems. Or other problems.

---------- Post updated at 08:29 ---------- Previous update was at 08:16 ----------

Corrected code, sort of:

Code:

#include <stdio.h>
#include <string.h>

void printit(char line_of_char[], int index);
int main()
{
   char line_of_char[80]={0x0};
   int index = -1;
   
   strcpy(line_of_char, "This is a string.");
   printit(line_of_char, index);
   printf("\n");
   return 0;
}
void printit(char line_of_char[], int index)
{
   if(index ==-1 || line_of_char[index])
   {   
   	index++;
    printf("+%c", line_of_char[index]); 
    printit(line_of_char, index);
    printf("-%c", line_of_char[index]);
   }
}

Last edited by jim mcnamara; 04-26-2010 at 11:23 AM..

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ssl_get_ex_data_x509_store_ctx_idx

SSL_get_ex_data_X509_STORE_CTX_idx(3SSL)			      OpenSSL				  SSL_get_ex_data_X509_STORE_CTX_idx(3SSL)

NAME

       SSL_get_ex_data_X509_STORE_CTX_idx - get ex_data index to access SSL structure from X509_STORE_CTX

SYNOPSIS

	#include <openssl/ssl.h>

	int SSL_get_ex_data_X509_STORE_CTX_idx(void);

DESCRIPTION

       SSL_get_ex_data_X509_STORE_CTX_idx() returns the index number under which the pointer to the SSL object is stored into the X509_STORE_CTX
       object.

NOTES

       Whenever a X509_STORE_CTX object is created for the verification of the peers certificate during a handshake, a pointer to the SSL object
       is stored into the X509_STORE_CTX object to identify the connection affected.  To retrieve this pointer the X509_STORE_CTX_get_ex_data()
       function can be used with the correct index. This index is globally the same for all X509_STORE_CTX objects and can be retrieved using
       SSL_get_ex_data_X509_STORE_CTX_idx(). The index value is set when SSL_get_ex_data_X509_STORE_CTX_idx() is first called either by the
       application program directly or indirectly during other SSL setup functions or during the handshake.

       The value depends on other index values defined for X509_STORE_CTX objects before the SSL index is created.

RETURN VALUES

       >=0 The index value to access the pointer.

       <0  An error occurred, check the error stack for a detailed error message.

EXAMPLES

       The index returned from SSL_get_ex_data_X509_STORE_CTX_idx() allows to access the SSL object for the connection to be accessed during the
       verify_callback() when checking the peers certificate. Please check the example in SSL_CTX_set_verify(3),

SEE ALSO

       ssl(3), SSL_CTX_set_verify(3), CRYPTO_set_ex_data(3)

1.0.1e								    2013-02-11				  SSL_get_ex_data_X509_STORE_CTX_idx(3SSL)

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