Conditional Statements

[Gregc.]

Hi

I am writing a conditional statement, using strcat. What I am trying
to do is to add the file extenstion '.txt' if it doesn't already exist.
What I am having trouble with is returning a value if one already
exists. Attached is the code below:

#include <stdio.h>
#include <string.h>
const int MAX_FILENAME = 256;
oid checkFilename (char *filename, char *extension)
{
int length;
int check;
length = strlen(filename);
check=strcmp(filename,extension);

if(check==0)
return;
else
strcat(filename,extension);

return;
int main () {
char filename1 [MAX_FILENAME] = "testfile";
char filename2 [MAX_FILENAME] = "testfile.txt";
char filename3 [MAX_FILENAME] = "testfile.dat";
char extension [] = ".txt";

checkFilename (filename1, extension);
checkFilename (filename2, extension);
checkFilename (filename3, extension);

printf("1: %s\n", filename1);
printf("2: %s\n", filename2);
printf("3: %s\n", filename3);
}

Could someone point me in the right direction.

Greg

[Zero]

Gregc. schrieb:

Hi

I am writing a conditional statement, using strcat. What I am trying
to do is to add the file extenstion '.txt' if it doesn't already exist.
What I am having trouble with is returning a value if one already
exists. Attached is the code below:

#include <stdio.h>
#include <string.h>
const int MAX_FILENAME = 256;
oid checkFilename (char *filename, char *extension)
{
int length;
int check;
length = strlen(filename);
check=strcmp(filename,extension);

if(check==0)
return;
else
strcat(filename,extension);

return;
int main () {
char filename1 [MAX_FILENAME] = "testfile";
char filename2 [MAX_FILENAME] = "testfile.txt";
char filename3 [MAX_FILENAME] = "testfile.dat";
char extension [] = ".txt";

checkFilename (filename1, extension);
checkFilename (filename2, extension);
checkFilename (filename3, extension);

printf("1: %s\n", filename1);
printf("2: %s\n", filename2);
printf("3: %s\n", filename3);
}

Could someone point me in the right direction.

Greg

One solution, which works but has to be checked clearly :)

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

#define MAX_FILENAME 256

void checkFilename (char *filename, char *extension)
{
int length;
int check;
char * pToString;

if(!strstr(filename,extension))
{
pToString = strchr(filename,'.');

if (pToString)
{
pToString[1] = 't';
pToString[2] = 'x';
pToString[3] = 't';
pToString[4] = '\0';
}
else
{
strcat(filename,extension);
}
}
}

int main () {

char filename1[MAX_FILENAME] = "testfile";
char filename2[MAX_FILENAME] = "testfile.txt";
char filename3[MAX_FILENAME] = "testfile.dat";

char extension [] = ".txt";

checkFilename (filename1, extension);
checkFilename (filename2, extension);
checkFilename (filename3, extension);
printf("1: %s\n", filename1);
printf("2: %s\n", filename2);
printf("3: %s\n", filename3);

getch();
}

[Abdo Haji-Ali]

Zero wrote:

One solution, which works but has to be checked clearly :)

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

#define MAX_FILENAME 256

void checkFilename (char *filename, char *extension)
{
int length;
int check;
char * pToString;

if(!strstr(filename,extension)) Consider the situation "BlatxtBla.ext"
{
pToString = strchr(filename,'.'); Consider the situation "Bla.Bla.ext"

if (pToString)
{
pToString[1] = 't';
pToString[2] = 'x';
pToString[3] = 't';
pToString[4] = '\0';
}
else
{
strcat(filename,extension); Consider the situation where the buffer is not big enough to hold the
extenstion
}
}
}

int main () {

char filename1[MAX_FILENAME] = "testfile";
char filename2[MAX_FILENAME] = "testfile.txt";
char filename3[MAX_FILENAME] = "testfile.dat";

char extension [] = ".txt";

checkFilename (filename1, extension);
checkFilename (filename2, extension);
checkFilename (filename3, extension);
printf("1: %s\n", filename1);
printf("2: %s\n", filename2);
printf("3: %s\n", filename3);

getch(); Where's the return statement?
}

Abdo Haji-Ali
Programmer
In|Framez

[CBFalconer]

"Gregc." wrote:

I am writing a conditional statement, using strcat. What I am
trying to do is to add the file extenstion '.txt' if it doesn't
already exist. What I am having trouble with is returning a
value if one already exists. Attached is the code below:

Look up strrchr() function.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>

[Fred Kleinschmidt]

"Abdo Haji-Ali" <ah***@inframez.com> wrote in message
news:11*********************@t31g2000cwb.googlegro ups.com...

Zero wrote:

One solution, which works but has to be checked clearly :)

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

#define MAX_FILENAME 256

void checkFilename (char *filename, char *extension, int maxlen)
{
int length;
int check;
char * pToString;

if(!strstr(filename,extension))

Consider the situation "BlatxtBla.ext"

{
pToString = strchr(filename,'.');

Consider the situation "Bla.Bla.ext"

if (pToString)
{
pToString[1] = 't';
pToString[2] = 'x';
pToString[3] = 't';
pToString[4] = '\0';
}
else
{
strcat(filename,extension);

Consider the situation where the buffer is not big enough to hold the
extenstion

}
}
}

int main () {

char filename1[MAX_FILENAME] = "testfile";
char filename2[MAX_FILENAME] = "testfile.txt";
char filename3[MAX_FILENAME] = "testfile.dat";

char extension [] = ".txt";

checkFilename (filename1, extension);
checkFilename (filename2, extension);
checkFilename (filename3, extension);
printf("1: %s\n", filename1);
printf("2: %s\n", filename2);
printf("3: %s\n", filename3);

getch();

Where's the return statement?

}

Abdo Haji-Ali
Programmer
In|Framez

checkFileName( filename, extension, MAX_FILENAME );

int checkFilename (char *filename, char *extension, int maxlen) {
size_t nchf, nche;
char *p = NULL;
if ( filename!=NULL && extension != NULL ) {
nche = strlen( extension);
nchf = strlen( filename );
if ( nchf > nche ) {
p = &filename[nchf-nche];
}
else {
p = filename;
}
if ( strcmp( p, extension ) != 0 ) {
if ( nchf+nche < maxlen ) {
strcpy( p, extension );
return 0; /* success */
}
}
}
return 1; /* failed to add extension */
}
--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Technical Architect, Software Reuse Project

[Abdo Haji-Ali]

Fred Kleinschmidt wrote:

int checkFilename (char *filename, char *extension, int maxlen) {
size_t nchf, nche;
char *p = NULL;
if ( filename!=NULL && extension != NULL ) {
nche = strlen( extension);
nchf = strlen( filename );
if ( nchf > nche ) {
p = &filename[nchf-nche];
}
else {
p = filename;
}
if ( strcmp( p, extension ) != 0 ) {
if ( nchf+nche < maxlen ) {
strcpy( p, extension );
return 0; /* success */
}
}
}
return 1; /* failed to add extension */
}

This function doesn't append the extention when necessary, it replaces
the last 'nche' (length of extenstion) characters of the file name with
the extension... Consider the situation when filename is "Blah" and the
extenstion is ".txt" the returned file name would be just ".txt";
which, I believe, isn't what the OP wanted.

Abdo Haji-Ali
Programmer
In|Framez

[Keith Thompson]

CBFalconer <cb********@yahoo.com> writes:

"Gregc." wrote:

I am writing a conditional statement, using strcat. What I am
trying to do is to add the file extenstion '.txt' if it doesn't
already exist. What I am having trouble with is returning a
value if one already exists. Attached is the code below:

Look up strrchr() function.

I'm not sure that strrchr() is going to be useful. It searches for a
single character; the OP wants to determine whether the name ends in a
specified string.

An outline of a solution:

If the name is less than 4 characters long, it doesn't end in
".txt".

Get a pointer to the fourth-to-last character of the string. Use
strcmp() to compare the (sub)string pointed to by that pointer to
".txt".

This is easily generalizable to arbitrary suffixes.

And if you append the ".txt", make sure you've allocated enough memory
to hold it.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Fred Kleinschmidt]

"Abdo Haji-Ali" <ah***@inframez.com> wrote in message
news:11**********************@j33g2000cwa.googlegr oups.com...

Fred Kleinschmidt wrote:

int checkFilename (char *filename, char *extension, int maxlen) {
size_t nchf, nche;
char *p = NULL;
if ( filename!=NULL && extension != NULL ) {
nche = strlen( extension);
nchf = strlen( filename );
if ( nchf > nche ) {
p = &filename[nchf-nche];
}
else {
p = filename;
}
if ( strcmp( p, extension ) != 0 ) {
if ( nchf+nche < maxlen ) {
strcpy( p, extension );
return 0; /* success */
}
}
}
return 1; /* failed to add extension */
}
This function doesn't append the extention when necessary, it replaces
the last 'nche' (length of extenstion) characters of the file name with
the extension... Consider the situation when filename is "Blah" and the
extenstion is ".txt" the returned file name would be just ".txt";
which, I believe, isn't what the OP wanted.

Oops - it should be
strcpy( filename, extension );

Abdo Haji-Ali
Programmer
In|Framez

--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Technical Architect, Software Reuse Project

[Abdo Haji-Ali]

Fred Kleinschmidt wrote:

"Abdo Haji-Ali" <ah***@inframez.com> wrote in message

This function doesn't append the extention when necessary, it replaces
the last 'nche' (length of extenstion) characters of the file name with
the extension... Consider the situation when filename is "Blah" and the
extenstion is ".txt" the returned file name would be just ".txt";
which, I believe, isn't what the OP wanted.

Oops - it should be
strcpy( filename, extension );

Which is even worse, it replaces the filename with the extension... I
think you meant:
strcat( p, extension );

Abdo Haji-Ali
Programmer
In|Framez

[Mark McIntyre]

On Wed, 26 Apr 2006 18:04:55 GMT, in comp.lang.c , Keith Thompson
<ks***@mib.org> wrote:

CBFalconer <cb********@yahoo.com> writes:

Look up strrchr() function.

I'm not sure that strrchr() is going to be useful. It searches for a
single character; the OP wants to determine whether the name ends in a
specified string.

starting with a dot. He can search for dots, and check that the
remaining part of the string a) has no more dots in it and b) is the
right pattern.

--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

[Keith Thompson]

Mark McIntyre <ma**********@spamcop.net> writes:

On Wed, 26 Apr 2006 18:04:55 GMT, in comp.lang.c , Keith Thompson
<ks***@mib.org> wrote:

CBFalconer <cb********@yahoo.com> writes:

Look up strrchr() function.

I'm not sure that strrchr() is going to be useful. It searches for a
single character; the OP wants to determine whether the name ends in a
specified string.

starting with a dot. He can search for dots, and check that the
remaining part of the string a) has no more dots in it and b) is the
right pattern.

That's useful if you're asking what extension a file name has. In
this case, the OP wanted to know specifically whether the file name
ends in ".txt"; in that case, there's nothing special about the '.'
character.

Yes, you could use the approach you suggest *in this case*, but it
doesn't generalize well to the problem of determining whether a string
ends in a specified substring. Consider determining whether a file
name ends in ".tar.gz"; if the file name is "foo.tar.gz", searching
for the last '.' misses the ".tar".

If you're always going to be looking for a suffix consisting of a '.'
followed by one or more additional characters that will never include
another '.', strrchr() might be useful. But personally, I'd rather
not hardwire that assumption into my code unless it makes things
significantly easier.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[August Karlstrom]

Gregc. wrote:

Hi

I am writing a conditional statement, using strcat. What I am trying
to do is to add the file extenstion '.txt' if it doesn't already exist.
What I am having trouble with is returning a value if one already
exists. Attached is the code below:

#include <stdio.h>
#include <string.h>
const int MAX_FILENAME = 256;
oid checkFilename (char *filename, char *extension)
{
int length;
int check;
length = strlen(filename);
check=strcmp(filename,extension);

if(check==0)
return;
else
strcat(filename,extension);

return;
int main () {
char filename1 [MAX_FILENAME] = "testfile";
char filename2 [MAX_FILENAME] = "testfile.txt";
char filename3 [MAX_FILENAME] = "testfile.dat";
char extension [] = ".txt";

checkFilename (filename1, extension);
checkFilename (filename2, extension);
checkFilename (filename3, extension);

printf("1: %s\n", filename1);
printf("2: %s\n", filename2);
printf("3: %s\n", filename3);
}

Could someone point me in the right direction.

I would do

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

#define FILENAME_LENGTH_MAX 256

/* Return a pointer to the start of the file extension (including the
dot) or a pointer to the string terminator if no extension is
found. */

char *extension(const char *filename)
{
char *result, *endp;

endp = filename + strlen(filename);
result = endp;
while ((result > filename) && (*result != '.'))
result--;
return (result == filename)? endp: result;
}
/* test */

int main(void)
{
char filename[FILENAME_LENGTH_MAX] = "testfile";
char *ext = ".txt";

if (strcmp(extension(filename), ext) != 0)
strcat(filename, ext);
puts(filename);
return 0;
}
August

[Walter Roberson]

In article <11**********************@y43g2000cwc.googlegroups .com>,
Gregc. <gr*********@bigpond.com> wrote:

What I am trying
to do is to add the file extenstion '.txt' if it doesn't already exist.

What is the result to be if the file name *is* '.txt' ?
--
"It is important to remember that when it comes to law, computers
never make copies, only human beings make copies. Computers are given
commands, not permission. Only people can be given permission."
-- Brad Templeton

[Gregc.]

Walter Roberson wrote:

What is the result to be if the file name *is* '.txt' ?
--

Then it will return testfile.txt ie no change.

[Keith Thompson]

"Gregc." <gr*********@bigpond.com> writes:

Walter Roberson wrote:

What is the result to be if the file name *is* '.txt' ?

Then it will return testfile.txt ie no change.

Don't you mean it will return ".txt"?

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Gregc.]

Keith Thompson wrote:

Don't you mean it will return ".txt"?

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

Yep, your correct. It's suppose to add .txt if one doesn't exist, and
it .txt already exist then there is no change.

[Walter Roberson]

In article <11**********************@e56g2000cwe.googlegroups .com>,
Gregc. <gr*********@bigpond.com> wrote:

Yep, your correct. It's suppose to add .txt if one doesn't exist, and
it .txt already exist then there is no change.

In the original problem statement, you phrased it in terms of
adding the file extension '.txt' if it was not already there.

For the file which is named just '.txt' with nothing else,
the base file name for which '.txt' would be the extension,
would be the empty filename. It is arguable that you have to
have a non-empty filename in order for '.txt' to be an
extension of that filename.

Not that it really matters to me whether '.txt' should be
left as is or changed to '.txt.txt'. I asked only because
I happened to notice some unusual logic in one of the suggested
implementations; when I traced the logic I realized it was
testing for this case, at which point I realized you had not
definitively indicated what should happen for it.

--
If you lie to the compiler, it will get its revenge. -- Henry Spencer

[Rod Pemberton]

"Gregc." <gr*********@bigpond.com> wrote in message
news:11**********************@y43g2000cwc.googlegr oups.com...

Hi

I am writing a conditional statement, using strcat. What I am trying
to do is to add the file extenstion '.txt' if it doesn't already exist.
What I am having trouble with is returning a value if one already
exists. Attached is the code below:

#include <stdio.h>
#include <string.h>
const int MAX_FILENAME = 256;
oid checkFilename (char *filename, char *extension)
{
int length;
int check;
length = strlen(filename);
check=strcmp(filename,extension);

if(check==0)
return;
else
strcat(filename,extension);

return;
int main () {
char filename1 [MAX_FILENAME] = "testfile";
char filename2 [MAX_FILENAME] = "testfile.txt";
char filename3 [MAX_FILENAME] = "testfile.dat";
char extension [] = ".txt";

checkFilename (filename1, extension);
checkFilename (filename2, extension);
checkFilename (filename3, extension);

printf("1: %s\n", filename1);
printf("2: %s\n", filename2);
printf("3: %s\n", filename3);
}

Could someone point me in the right direction.

Yes, I think the following is closer to what you want.
#include <stdio.h>
#include <string.h>

typedef unsigned int oid;
const int MAX_FILENAME = 256;

oid checkFilename (char *filename, char *extension)
{
int check=0;

if(strchr(filename,'.')==NULL) /* no period, so no extension */
{
strcat(filename,extension);
check=1;
}
else /* possible extension */
{
if(!strcmp(strchr(filename,'.'),&extension[1]))
{ /* no matching extension */
strcat(filename,extension);
check=1;
}
}

if(check==0)
return(1);

return(0);
}

int main(void)
{
char filename1[MAX_FILENAME];
char filename2[MAX_FILENAME];
char filename3[MAX_FILENAME];
char extension[] = ".txt";
unsigned int error;

strcpy(filename1,"testfile");
strcpy(filename2,"testfile.txt");
strcpy(filename3,"testfile.dat");

error=checkFilename (filename1, extension);
printf("1:%d| %s\n",error, filename1);

error=checkFilename (filename2, extension);
printf("2:%d| %s\n",error, filename2);

error=checkFilename (filename3, extension);
printf("3:%d| %s\n",error,filename3);
}
Rod Pemberton