Bizarre char* problem

[the.tarquin]

Okay, this one has me totally baffled. I have a function,
getParsedKey(ch ar* key, char* returnString). I pass in the key I want,
it retrieves it from a data structure and puts the value in
returnString. The problem is that returnString points to the correct
value in the function, but after the function has finished, the string
that it points to is empty.

.....
char* radioList = NULL;
ini->getParsedKey(" Radio",radioLis t);
.....

bool iniparser::getP arsedKey(char *key, char *returnString)
{
//for all the keys in the section
for (int i = 0; i < numKeysInSectio n; i++)
{
//returnString takes the value of the current key
returnString = strtok(iniSecti on[i],"=");
//if the current key is the desired key
if ((strcmp(return String,key) == 0))
{
//then returnString takes on the key's value
returnString = strtok(NULL,"\n ");
MessageBox(NULL ,returnString," returnString in
getParsedKey(2) ",NULL);
//return the key's value
return true;
}
}

MessageBox(NULL ,"KEY NOT FOUND","OK",NUL L);
//if the key isn't found, return NULL
return false;
}

So, to clarify, radiolist gets passed to getParsedKey, which finds the
key "Radio" and puts the value assosciated with radio in the pointer.
While it's in the function, the pointer (returnString) points, as it
should, to the value. After the function has finished, however, the
pointer radioList points to an empty string. This has me totally
baffled. I'm hoping I've made a noob mistake somewhere in the code and
that someone can kindly point it out to me, because I've been staring
at this and poking at it for many, many hours now, to no avail.

Any suggestions?

Cheers,
Aaron Brown

P.S: I'm working in the Visual Studio 2005 IDE

[Victor Bazarov]

th*********@gma il.com wrote:

Okay, this one has me totally baffled. I have a function,
getParsedKey(ch ar* key, char* returnString). I pass in the key I
want, it retrieves it from a data structure and puts the value in
returnString. The problem is that returnString points to the correct
value in the function, but after the function has finished, the string
that it points to is empty.

....
char* radioList = NULL;
ini->getParsedKey(" Radio",radioLis t);
....

bool iniparser::getP arsedKey(char *key, char *returnString)
{
//for all the keys in the section
for (int i = 0; i < numKeysInSectio n; i++)
{
//returnString takes the value of the current key
returnString = strtok(iniSecti on[i],"=");
You change the *local* pointer here. This action has nothing to do
with the variable that you passed in.
//if the current key is the desired key
if ((strcmp(return String,key) == 0))
{
//then returnString takes on the key's value
returnString = strtok(NULL,"\n ");
Again...
MessageBox(NULL ,returnString," returnString in
getParsedKey(2) ",NULL);
You have 'newline' in a literal here...
//return the key's value
return true;
}
}

MessageBox(NULL ,"KEY NOT FOUND","OK",NUL L);
//if the key isn't found, return NULL
return false;
}

So, to clarify, radiolist gets passed to getParsedKey, which finds the
key "Radio" and puts the value assosciated with radio in the pointer.
While it's in the function, the pointer (returnString) points, as it
should, to the value. After the function has finished, however, the
pointer radioList points to an empty string. This has me totally
baffled.
How about this:

foo(char const * blah)
{
blah = "DEF";
}

#include <stdio.h>
int main()
{
const char * blah = "ABC";
printf(blah);
}

? Confusing as well?
I'm hoping I've made a noob mistake somewhere in the code
and that someone can kindly point it out to me, because I've been
staring at this and poking at it for many, many hours now, to no
avail.

Any suggestions?
Don't use plain pointers. Or pass the second argument by reference.

Cheers,
Aaron Brown

P.S: I'm working in the Visual Studio 2005 IDE

If you need a VC++-specific solution, you might want to post to
'microsoft.publ ic.vc.language' newsgroup.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Default User]

th*********@gma il.com wrote:

Okay, this one has me totally baffled. I have a function,
getParsedKey(ch ar* key, char* returnString). I pass in the key I
want, it retrieves it from a data structure and puts the value in
returnString. The problem is that returnString points to the correct
value in the function, but after the function has finished, the string
that it points to is empty.

Look at the follow program. What do you think the value of i in main()
will be after the call to func()?

void func(int n)
{
n = 3;
}
int main()
{
int i = 0;

func(i);

return 0;
}

Brian

[Roberto Waltman]

<th*********@gm ail.com> wrote:

... I have a function,
getParsedKey(c har* key, char* returnString). I pass in the key I want,
it retrieves it from a data structure and puts the value in
returnString . The problem is that returnString points to the correct
value in the function, but after the function has finished, the string
that it points to is empty.
...
bool iniparser::getP arsedKey(char *key, char *returnString)
{
...
returnString = strtok(NULL,"\n ");
...
}
...
Any suggestions?

You are modifying only a local copy of returnString.

[Noah Roberts]

Default User wrote:

th*********@gma il.com wrote:

Okay, this one has me totally baffled. I have a function,
getParsedKey(ch ar* key, char* returnString). I pass in the key I
want, it retrieves it from a data structure and puts the value in
returnString. The problem is that returnString points to the correct
value in the function, but after the function has finished, the string
that it points to is empty.

Look at the follow program. What do you think the value of i in main()
will be after the call to func()?

void func(int n)
{
n = 3;
}
int main()
{
int i = 0;

func(i);

return 0;
}

5?

[the.tarquin]

You're all quite correct. I modified it so that, instead of passing in
a pointer by value I had it return a pointer to the correct string.
This, unfortunately, didn't solve the problem.

....
char* radioList = ini->getParsedKey(" Radio");
....

char* iniparser::getP arsedKey(char* keyName)
{
char* tempString = new char[MAX_INI_LINE_LE NGTH];
for(int i = 0; i < strlen(keyName) ; i++)
{
tolower(keyName[i]);
}

//for all the keys in the section
for (int i = 0; i < numKeysInSectio n; i++)
{
//tempString takes the value of the current key
tempString = strtok(iniSecti on[i],"=");
//if the current key is the desired key
if ((strcmp(tempSt ring,keyName) == 0))
{
//then tempString takes on the key's value
tempString = strtok(NULL,"\n ");
//return the key's value
return tempString;
}
}

MessageBox(NULL ,"KEY NOT FOUND","OK",NUL L);
//if the key isn't found, return NULL
return NULL;
}

Now, correct me if I'm wrong, but that should fix the pass-by-value
problem of the previous version of this function, right? I mean, I'm
passing back an address to a character string. That character string
exists inside the function, but disappears once the function has
returned the pointer.
Roberto Waltman wrote:

<th*********@gm ail.com> wrote:

... I have a function,
getParsedKey(c har* key, char* returnString). I pass in the key I want,
it retrieves it from a data structure and puts the value in
returnString . The problem is that returnString points to the correct
value in the function, but after the function has finished, the string
that it points to is empty.
...
bool iniparser::getP arsedKey(char *key, char *returnString)
{
...
returnString = strtok(NULL,"\n ");
...
}
...
Any suggestions?

You are modifying only a local copy of returnString.

[Default User]

Noah Roberts wrote:

Default User wrote:

Look at the follow program. What do you think the value of i in
main() will be after the call to func()?

void func(int n)
{
n = 3;
}
int main()
{
int i = 0;

func(i);

return 0;
}

5?

You may want to look into another occupation. ;)


Brian

[Default User]

th*********@gma il.com wrote:

You're all quite correct. I modified it so that, instead of passing
in a pointer by value I had it return a pointer to the correct string.
This, unfortunately, didn't solve the problem.
Don't top-post. Your replies belong following or interspersed with
trimmed quotes.

...
char* radioList = ini->getParsedKey(" Radio");
...

char* iniparser::getP arsedKey(char* keyName)
{
char* tempString = new char[MAX_INI_LINE_LE NGTH];
for(int i = 0; i < strlen(keyName) ; i++)
{
tolower(keyName[i]);
}

You are attempting to modify a string literal. That causes undefined
behavior.

Is there a reason you aren't using std::string?


Brian

[mangesh]

just change function prototype to

char* iniparser::getP arsedKey(char[] keyName) ;

This will solve your problem

Regards
mangesh

[Thomas J. Gritzan]

mangesh schrieb:

just change function prototype to

char* iniparser::getP arsedKey(char[] keyName) ;

This will solve your problem

Please quote what yuo are referring to.

The original prototype is

char* iniparser::getP arsedKey(char* keyName);

So what problem will the char[] solve? Its functionally equal.

Thomas