Having problems returning a char* from a function..need help...

[LongBow]

Hello all,

From doing a google serach in the newsgroups I found out that a
string can't be returned from a function, but using a char* I should
be able to do it. I have spent most of the day trying to get this to
work, but been unable to solve my mistake. What the function should
return is a file name used for creating logs files. It will look
something like

JN122345.log

JN - Month
12 - Date
23 - Hour
45 - Min

Can anyone provide any assistance, please. Thanks!.

Mark
--------- source code ------------

#define MAX_TIME_LEN 6

char cMonths[12][2] = { "JN", "FB", "MR", "AP", "MY", "JU",
"JL", "AG", "SP", "OC", "NV", "DC" };
main( argc, argv )
int argc;
char *argv[];
{
char fileName[80];

*sAutoBITELogFi leName = getAutoBITELogF ileName( );

// Just seems to print only on character.
_settextpositio n( 1,1 );
printf( "lfn: '%s'", sAutoBITELogFil eName );

}

char *getAutoBITELog FileName( )
{
/*----------------------------------------
%d Day (01-31)
%H Hour 24-hour style (00-23)
%M Minute (00-59)
------------------------------------------*/

time_t currentTime;
struct tm* daynow;
int iResult;
char cTemp[ MAX_TIME_LEN + 1 ];
char *fileName;

/*sizeof *fileName is always 1, multiply by it anyway*/
fileName = malloc( 13 * sizeof(*fileNam e) );

if ( fileName == NULL ) {
return NULL; // Problem allocating memory
}

currentTime = time(NULL); // get the current arithmetic calendar
time

// Convert the current arithmetic calendar time into local time held
in a
// structure of type tm.
daynow = localtime(&curr entTime);

strncpy( fileName, cMonths[daynow->tm_mon], 2 );

iResult = strftime(cTemp, MAX_TIME_LEN + 1, "%d%H%M", daynow);

// Check to see if there was an error
if ( iResult == 0 ) {
return NULL;
}

strncat( fileName, cTemp, 6 );
strncat( fileName, ".log", 4 );

// Generally prints garbage, but some times can see the filename.
_settextpositio n( 25, 1 );
printf( "fn: %s", &fileName );

return (char *)fileName;
}

[Irrwahn Grausewitz]

LongBow <pi***@mud.pool > wrote:

Hello all,

From doing a google serach in the newsgroups I found out that a
string can't be returned from a function, but using a char* I should
be able to do it. I have spent most of the day trying to get this to
work, but been unable to solve my mistake. What the function should
return is a file name used for creating logs files. It will look
something like

JN122345.log

JN - Month
12 - Date
23 - Hour
45 - Min

Can anyone provide any assistance, please. Thanks!.

Mark
--------- source code ------------ /* You failed to include those: */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define MAX_TIME_LEN 6

char cMonths[12][2] = { "JN", "FB", "MR", "AP", "MY", "JU",
"JL", "AG", "SP", "OC", "NV", "DC" };

/* You failed to provide a prototype: */
char *getAutoBITELog FileName( );

main( argc, argv )
int argc;
char *argv[]; int main( void ) /* you don't use argc and argv */
{
char fileName[80]; /* You declare an array of characters without using it. */
*sAutoBITELogFi leName = getAutoBITELogF ileName( ); /* You failed to declare sAutoBITELogFil eName. */

// Just seems to print only on character.
_settextpositio n( 1,1 ); /* Non-standard. No idea. */
printf( "lfn: '%s'", sAutoBITELogFil eName );
/* You failed to return a value from a function
declared to returning int: */

return 0;}

char *getAutoBITELog FileName( )
{
/*----------------------------------------
%d Day (01-31)
%H Hour 24-hour style (00-23)
%M Minute (00-59)
------------------------------------------*/

time_t currentTime;
struct tm* daynow;
int iResult;
char cTemp[ MAX_TIME_LEN + 1 ];
char *fileName;

/*sizeof *fileName is always 1, multiply by it anyway*/
fileName = malloc( 13 * sizeof(*fileNam e) ); Magic number 13.

if ( fileName == NULL ) {
return NULL; // Problem allocating memory
}

currentTime = time(NULL); // get the current arithmetic calendar
time

// Convert the current arithmetic calendar time into local time held
in a
// structure of type tm.
daynow = localtime(&curr entTime);

strncpy( fileName, cMonths[daynow->tm_mon], 2 );

iResult = strftime(cTemp, MAX_TIME_LEN + 1, "%d%H%M", daynow);

// Check to see if there was an error
if ( iResult == 0 ) {
return NULL;
}

strncat( fileName, cTemp, 6 );
strncat( fileName, ".log", 4 );

// Generally prints garbage, but some times can see the filename.
_settextpositio n( 25, 1 ); Non-standard. No idea.
printf( "fn: %s", &fileName ); printf( "fn: %s", fileName );

return (char *)fileName; return fileName;
}

Please read the faq-list for c.l.c at:
http://www.eskimo.com/~scs/C-faq/top.html

Irrwahn
--
Posting in usenet is like playing golf in a mine-field.

[T.M. Sommers]

LongBow wrote:

Hello all,

From doing a google serach in the newsgroups I found out that a
string can't be returned from a function, but using a char* I should
be able to do it. I have spent most of the day trying to get this to
work, but been unable to solve my mistake. What the function should
return is a file name used for creating logs files. It will look
something like

JN122345.log

JN - Month
12 - Date
23 - Hour
45 - Min

Can anyone provide any assistance, please. Thanks!.

Mark
--------- source code ------------

#define MAX_TIME_LEN 6

char cMonths[12][2] = { "JN", "FB", "MR", "AP", "MY", "JU",
"JL", "AG", "SP", "OC", "NV", "DC" };
#include <stdio.h>
#include <time.h>
#include <stdlib.h>

char *getAutoBITELog FileName( );

To avoid the implicit int.
main( argc, argv )
int argc;
char *argv[];
int main(int argc, char *argv[])
{
char fileName[80];

*sAutoBITELogFi leName = getAutoBITELogF ileName( );

// Just seems to print only on character.
_settextpositio n( 1,1 );
Non-standard.
printf( "lfn: '%s'", sAutoBITELogFil eName );
printf( "lfn: '%s'\n", sAutoBITELogFil eName );

Add a newline to improve readability of the output.

}

char *getAutoBITELog FileName( )
{
/*----------------------------------------
%d Day (01-31)
%H Hour 24-hour style (00-23)
%M Minute (00-59)
------------------------------------------*/

time_t currentTime;
struct tm* daynow;
int iResult;
char cTemp[ MAX_TIME_LEN + 1 ];
char *fileName;

/*sizeof *fileName is always 1, multiply by it anyway*/
fileName = malloc( 13 * sizeof(*fileNam e) );

if ( fileName == NULL ) {
return NULL; // Problem allocating memory
}

currentTime = time(NULL); // get the current arithmetic calendar
time

// Convert the current arithmetic calendar time into local time held
in a
// structure of type tm.
daynow = localtime(&curr entTime);

strncpy( fileName, cMonths[daynow->tm_mon], 2 );

iResult = strftime(cTemp, MAX_TIME_LEN + 1, "%d%H%M", daynow);

// Check to see if there was an error
if ( iResult == 0 ) {
return NULL;
}

strncat( fileName, cTemp, 6 );
strncat( fileName, ".log", 4 );

// Generally prints garbage, but some times can see the filename.
_settextpositio n( 25, 1 );
Non-standard.
printf( "fn: %s", &fileName );
printf( "fn: %s\n", fileName );

Add a newline, and you don't want to print the address of fileName,
you want to print the contents. If you had turned all warnings on in
your compiler, it should have caught this and the implicit ints.

return (char *)fileName;
The cast is redundant; fileName is already a char *.
}

[Irrwahn Grausewitz]

"T.M. Sommers" <tm**@mail.ptd. net> wrote:

LongBow wrote:

<BIG SNIP>

printf( "fn: %s", &fileName );

printf( "fn: %s\n", fileName );

Add a newline, and you don't want to print the address of fileName,
you want to print the contents. If you had turned all warnings on in
your compiler, it should have caught this and the implicit ints.

If he had even tried to compile it, the compiler would have presented
a fine (and long) list of errors and warnings, pointing out what is
wrong.

8^)

Irrwahn

--
do not write: void main(...)
do not cast the return value of malloc()
do not fflush( stdin )
read the c.l.c-faq: http://www.eskimo.com/~scs/C-faq/top.html

[LongBow]

Irrwahn,

Sorry, I cut and pasted for the purpose of this posting since I
didn't want to include everything. I also failed to mention that I am
using Microsoft C v6.00 and I am modifying an existing code base. So
the main declaration is correct. The include files are there is the
prototype in the header file, but not listed in the posting. The
_settextpositio n sets the cursor position on the screen. When
declaring fileName in the main, it should have been
sAutoBITELogFil eName, but I cut and paste the wrong item.

Perhaps it is best to repost the code with the header files this
time.. I hope this is better this time around.. sorry for the first
bad posting..

Mark

--------- start main.h ---------------

// Only relevant items listed for posting

#include <stdio.h>
#include <conio.h>
#include <graph.h>
#include <switches.h>
#include <time.h>

#define MAX_TIME_LEN 6

char cMonths[12][2] = { "JN", "FB", "MR", "AP", "MY", "JU",
"JL", "AG", "SP", "OC", "NV", "DC" };

--------- end main.h ---------------

--------- start main.c ---------------

// Only relevant items listed for posting

#include "main.h"

main( argc, argv )
int argc;
char *argv[];
{

// Declare the Log File variable
char sAutoBITELogFil eName[80];

// Current a log file name
*sAutoBITELogFi leName = getAutoBITELogF ileName( );

// Set the cursor position then print the resultant string
_settextpositio n( 1,1 );
printf( "lfn: '%s'", sAutoBITELogFil eName );

return 0;
}

char *getAutoBITELog FileName( )
{
/*----------------------------------------
%d Day (01-31)
%H Hour 24-hour style (00-23)
%M Minute (00-59)
------------------------------------------*/

time_t currentTime;
struct tm* daynow;
int iResult;
char cTemp[ MAX_TIME_LEN + 1 ];
char *fileName;

/*sizeof *fileName is always 1, multiply by it anyway*/
// DOS file name is 8 dot 3 for a total of 12 characters plus
// a null terminating character. It will be defined later.

fileName = malloc( 13 * sizeof(*fileNam e) );
if ( fileName == NULL ) {
return NULL; // Problem allocating memory
}

currentTime = time(NULL); // get the current arithmetic calendar
time

// Convert the current arithmetic calendar time into local time held
in a
// structure of type tm.
daynow = localtime(&curr entTime);

strncpy( fileName, cMonths[daynow->tm_mon], 2 );

// MAX_TIME_LEN is 6 since the format of the file name is
MONTH/DATE/HOUR/MIN
// which are all two character for a total of 8. So 8 minus two for
the 6 with
// a null terminating character.
iResult = strftime(cTemp, MAX_TIME_LEN + 1, "%d%H%M", daynow);

// Check to see if there was an error
if ( iResult == 0 ) {
return NULL;
}

strncat( fileName, cTemp, 6 );
strncat( fileName, ".log", 4 );

_settextpositio n( 25, 1 );
printf( "fn: %s", fileName );

return fileName;
}

--------- end main.c ---------------

[LongBow]

If he had even tried to compile it, the compiler would have presented
a fine (and long) list of errors and warnings, pointing out what is
wrong.

8^)

No compiler errors, I do get two warnings at these points which are
both

'=' : different levels of indirection

One in main at this point

the other warning is point in between these two lines, not sure which
one. I have compiled the project several times, but always in between
these two lines..
fileName = malloc( 13 * sizeof(*fileNam e) );
<--- points here.....
if ( fileName == NULL )
I am not to sure what it means, but if someone does can you please
tell me. thanks

Mark

[LongBow]

If he had even tried to compile it, the compiler would have presented
a fine (and long) list of errors and warnings, pointing out what is
wrong.

8^)

No compiler errors, I do get two warnings at these points which are
both

'=' : different levels of indirection

One in main at this point

*sAutoBITELogFi leName = getAutoBITELogF ileName( );
the other warning is point in between these two lines, not sure which
one. I have compiled the project several times, but always in between
these two lines..
fileName = malloc( 13 * sizeof(*fileNam e) );
<--- points here.....
if ( fileName == NULL )
I am not to sure what it means, but if someone does can you please
tell me. thanks

Mark

[Irrwahn Grausewitz]

LongBow <pi***@mud.pool > wrote:

Irrwahn,

Sorry, I cut and pasted for the purpose of this posting since I
didn't want to include everything. I also failed to mention that I am
using Microsoft C v6.00 and I am modifying an existing code base. So
the main declaration is correct. The include files are there is the
prototype in the header file, but not listed in the posting. The
_settextpositi on sets the cursor position on the screen. When
declaring fileName in the main, it should have been
sAutoBITELogFi leName, but I cut and paste the wrong item.

Perhaps it is best to repost the code with the header files this
time.. I hope this is better this time around.. sorry for the first
bad posting..

Mark

--------- start main.h ---------------

// Only relevant items listed for posting

#include <stdio.h> #include <conio.h>
#include <graph.h>
#include <switches.h> Well, posting code using non-standard extensions to the C language
is still something that is frowned upon here in comp.lang.c.
For example, my implementation does not provide these headers, so
I have to delete all this stuff in order to compile your code ...
#include <time.h> #include <stdlib.h> /* for malloc() */
#include <string.h> /* for strcpy() and strcat() */

#define MAX_TIME_LEN 6

char cMonths[12][2] = { "JN", "FB", "MR", "AP", "MY", "JU",
"JL", "AG", "SP", "OC", "NV", "DC" };

--------- end main.h ---------------

--------- start main.c ---------------

// Only relevant items listed for posting Unfortunately, not quite. ;-)

Oh, and one more hint: single-line comments are likely to produce
confusion in that they tend to produce funny effects when line
wrapping occurs in the news-reader...

#include "main.h"
Provide a prototype for getAutoBITELogF ileName():

char *getAutoBITELog FileName();

main( argc, argv )
int argc;
char *argv[];
{

// Declare the Log File variable
char sAutoBITELogFil eName[80]; You allocate memory for the filename in getAutoBITELogF ileName(), so:
char *sAutoBITELogFi leName;

[ Or keep the array, assign the result of getAutoBITELogF ileName() to
a temporary variable, strcpy() the string to sAutoBITELogFil eName
and free() the memory you allocated using the temporary variable ]

// Current a log file name
*sAutoBITELogFi leName = getAutoBITELogF ileName( );

Get rid of the '*'.

<SNIP>

After performing a quick clean-up, your code looks like this:

/*************** *************** *************** ***/

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

#define MAX_TIME_LEN 6

char cMonths[12][2] = { "JN", "FB", "MR", "AP", "MY", "JU",
"JL", "AG", "SP", "OC", "NV", "DC" };

/* provide a prototype for getAutoBITELogF ileName() */
char *getAutoBITELog FileName();

int main( )
{
char *sAutoBITELogFi leName;

sAutoBITELogFil eName = getAutoBITELogF ileName( );

printf( "lfn: '%s'", sAutoBITELogFil eName );
fflush( stdout );
return 0;
}

char *getAutoBITELog FileName( )
{
time_t currentTime;
struct tm* daynow;
int iResult;
char cTemp[ MAX_TIME_LEN + 1 ];
char *fileName;

/*sizeof *fileName is always 1, multiply by it anyway
DOS file name is 8 dot 3 for a total of 12 characters plus
a null terminating character. It will be defined later. */

fileName = malloc( 13 * sizeof(*fileNam e) );

if ( fileName == NULL ) {
return NULL; /* Problem allocating memory */
}

/* get the current arithmetic calendar time */
currentTime = time(NULL);

/* Convert the current arithmetic calendar time into local
time held in a structure of type tm. */
daynow = localtime(&curr entTime);

strncpy( fileName, cMonths[daynow->tm_mon], 2 );

/* MAX_TIME_LEN is 6 since the format of the file name is
MONTH/DATE/HOUR/MIN which are all two character for a
total of 8. So 8 minus two for the 6 with a null
terminating character.*/

iResult = strftime(cTemp, MAX_TIME_LEN + 1, "%d%H%M", daynow);

/* Check to see if there was an error */
if ( iResult == 0 ) {
return NULL;
}

strncat( fileName, cTemp, 6 );
strncat( fileName, ".log", 4 );

printf( "fn: %s ", fileName );

return fileName;
}

/*************** *************** *************** ***/

IMHO, this version should be fairly portable and AFAICS works fine,
though I have not tested it thoroughly. However, there is still room
for some improvements, but unfortunately I have to go and get some
sleep right now, but hopefully someone else will take over at this
point...

Regards

Irrwahn
--
Zzzzzzzzzzz-Roooooooon

[LongBow]

Irrwahn,

The solution you provide didn't work fully, but compiled without
warning nor errors, but it was still returning a bad string value.
After several hours I have a working version, but testing is still
needed and I may have tweak it since I got a solution working Visual
C++ v6.0. I need the IDE to trace through the code to see what was
going on. There is one important note in the documentation that
pointed me in the right direction since I was seeing the char strings
larger than what I was specifying during allocation.

---- Taken from MSDN April 2001 under 'malloc' ----
Remarks
The malloc function allocates a memory block of at least size bytes.
The block may be larger than size bytes because of space required for
alignment and maintenance information.

Since the malloc was creating a memory block and larger than I
specified. In addition the memory block was fully of junk so during
the string operation it wasn't finding the NULL character in the
correct locations. So I needed to clear the memory block. At first I
was using _strset, but it was causing access violation when the heap
was freed. I found the function memset which allows me to specify the
length. Thanks for the help and pointing me in the right direction.
Sorry for posting in the wrong group, but I couldn't find another
group under microsoft.publi c.* domain, at least what my ISP news
servers list. I figure people wouldn't mind.....

Mark
here is what I have thus far for those who want to see. Compile and
ran under Visual C++ v6.0 ( VS 97 )....

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#define MAX_TIME_LEN 6
#define MAX_FILE_NAME_L ENGTH 12
#define FILE_NAME_EXT ".log"

char cMonths[12][2] = { "JN", "FB", "MR", "AP", "MY", "JU",
"JL", "AG", "SP", "OC", "NV", "DC" };

/* provide a prototype for getAutoBITELogF ileName() */
int getAutoBITELogF ileName( char *fileName );

int main( )
{
char *sAutoBITELogFi leName;
int iResult;

sAutoBITELogFil eName = malloc( MAX_FILE_NAME_L ENGTH + 5 );
_strset( sAutoBITELogFil eName, 0 );

iResult = getAutoBITELogF ileName( sAutoBITELogFil eName );
printf( "lfn: '%s'\n\n", sAutoBITELogFil eName );
fflush( stdout );
return 0;
}

int getAutoBITELogF ileName( char *fileName )
{
time_t currentTime;
struct tm* daynow;
int iResult;
char cTemp[ MAX_TIME_LEN + 1 ];
char *tempFileName;

/*sizeof *fileName is always 1, multiply by it anyway
DOS file name is 8 dot 3 for a total of 12 characters plus
a null terminating character. It will be defined later. */

tempFileName = malloc( MAX_FILE_NAME_L ENGTH + 1 );

memset( tempFileName, 0, MAX_FILE_NAME_L ENGTH + 1 );
memset( cTemp, 0, MAX_TIME_LEN + 1 );

if ( tempFileName == NULL ) {
return 0; /* Problem allocating memory */
}

/* get the current arithmetic calendar time */
currentTime = time(NULL);

/* Convert the current arithmetic calendar time into local
time held in a structure of type tm. */
daynow = localtime(&curr entTime);

strncpy( tempFileName, cMonths[daynow->tm_mon], 2 );

/* MAX_TIME_LEN is 6 since the format of the file name is
MONTH/DATE/HOUR/MIN which are all two character for a
total of 8. So 8 minus two for the 6 with a null
terminating character.*/

iResult = strftime(cTemp, MAX_TIME_LEN + 1, "%d%H%M", daynow);

/* Check to see if there was an error */
if ( iResult == 0 ) {
return 0;
}

strncat( tempFileName, cTemp, MAX_TIME_LEN );
strncat( tempFileName, FILE_NAME_EXT, sizeof( FILE_NAME_EXT ) );
strcpy( fileName, tempFileName );

iResult = strlen( tempFileName );
free( tempFileName );

return iResult;

}

[Tom Zych]

LongBow wrote:

main( argc, argv )
int argc;
char *argv[];
{

This style of function definition, though still supported, has been
obsolete for about 15 years. What book did you learn this from?

--
Tom Zych
This email address will expire at some point to thwart spammers.
Permanent address: echo 'g******@cbobk. pbz' | rot13