Newbie. Microsoft Visual Express 2008. Problem with Assignment

[HansWernerMarschke@web.de]

// This will be a simple example for Matlab programming in C
// But I have to first test the C program before I incorporate it into
Matlab

char *encrypt_string (char *string)
{
unsigned int i;
// Allocate memory
char *encrypted_stri ng = (char *)
malloc(strlen(s tring)*sizeof(c har));
// Encrypt the string
for (i = 0; i < strlen(string); ++i)
{
encrypted_strin g[i] = encrypt_char(st ring[i]);
}
encrypted_strin g[i] = "\0"; <------------- Something goes wrong
warning C4047
return encrypted_strin g;
}

------------------Anzahl der Dereferenzierun gen bei 'char' und 'char
[2]' unterschiedlich

[Walter Roberson]

Re: Newbie. Microsoft Visual Express 2008. Problem with Assignment

In article <d255244f-467b-4dce-8b86-e92061d0a663@34 g2000hsh.google groups.com>,
<HansWernerMars chke@web.dewrot e:

char *encrypted_stri ng = (char *)
>malloc(strlen( string)*sizeof( char));

> encrypted_strin g[i] = "\0"; <------------- Something goes wrong

encrypted_strin g[i] = '\0';
OR
encrypted_strin g[i] = 0;

"\0" is a string, which devolves to a pointer to the string,
so you are trying to store a pointer in a char.
--
"The first draught serveth for health, the second for pleasure,
the third for shame, the fourth for madness." -- Sir Walter Raleigh

[Barry Schwarz]

Re: Newbie. Microsoft Visual Express 2008. Problem with Assignment

On Thu, 24 Apr 2008 15:26:48 -0700 (PDT), HansWernerMarsc hke@web.de
wrote:

>// This will be a simple example for Matlab programming in C
>// But I have to first test the C program before I incorporate it into
>Matlab
>
>char *encrypt_string (char *string)
>{
unsigned int i;
// Allocate memory
char *encrypted_stri ng = (char *)
>malloc(strlen( string)*sizeof( char));
// Encrypt the string
for (i = 0; i < strlen(string); ++i)
{
encrypted_strin g[i] = encrypt_char(st ring[i]);
}
> encrypted_strin g[i] = "\0"; <------------- Something goes wrong
>warning C4047
return encrypted_strin g;
>}

The syntax error is because you should have used single quotes(')
instead of double quotes("). However, after that is fixed, the
statement invokes undefined behavior because you did not malloc enough
space. strlen(string)* sizeof(char) evaluates to enough bytes to hold
the encrypted data except for the terminal '\0'. You need to add one
to the expression to make room for the '\0'.


Remove del for email

[lawrence.jones@siemens.com]

Re: Newbie. Microsoft Visual Express 2008. Problem with Assignment

HansWernerMarsc hke@web.de wrote:

>
char *encrypt_string (char *string)
{
unsigned int i;
// Allocate memory
char *encrypted_stri ng = (char *)
malloc(strlen(s tring)*sizeof(c har));

Casting the return value of malloc in C is generally considered to
be a bad idea. Be sure to #include <stdlib.hand <string.hto get
appropriate declarations for the library functions you're using.

sizeof(char) is 1, by definition.

You need to add 1 more to the size you're allocating to have room to
store the null terminator.

-Larry Jones

I always send Grandma a thank-you note right away. ...Ever since she
sent me that empty box with the sarcastic note saying she was just
checking to see if the Postal Service was still working. -- Calvin