Char to char*?

[Sona]

Hi,

How is it possible to convert a char to char* in C? I'm trying to append
a char to the end of a char* using the strcat function.. the following
however is not working:

char* s1, *s2;
char* result;
....

....
result = strcat(s1, (const char*)s2[3]); // application crashes here

What am I doing wrong? thanks

Sona

[Ben Pfaff]

Sona <so**********@nospam.com> writes:

How is it possible to convert a char to char* in C? I'm trying to
append a char to the end of a char* using the strcat function.. the
following however is not working:

char* s1, *s2;
char* result;
...

...
result = strcat(s1, (const char*)s2[3]); // application crashes here

The second argument of strcat() is a const char *. You are
passing a character. The cast to const char * is not going to
help.

You will have to construct a real string:

char tempstr[2];

tempstr[0] = s2[3];
tempstr[1] = '\0';
strcat(s1, tempstr);
--
"C has its problems, but a language designed from scratch would have some too,
and we know C's problems."
--Bjarne Stroustrup

[Martin Ambuhl]

Sona wrote:

Hi,

How is it possible to convert a char to char* in C? I'm trying to append
a char to the end of a char* using the strcat function.. the following
however is not working:

char* s1, *s2;
char* result;
...

...
result = strcat(s1, (const char*)s2[3]); // application crashes here

What am I doing wrong? thanks

Being confused; no shame is attached to that. Try this, which seems to be
what you are trying:

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

#define STRsize 256

int main(void)
{
char base[STRsize] = "base+";
char other[STRsize] = "xxxayyy";
/* appending a character from a string */
strncat(base, other + 3, 1);
printf("%s\n", base);
return 0;
}

[output]
base+a


--
Martin Ambuhl

[Default User]

Ben Pfaff wrote:

Sona <so**********@nospam.com> writes:

...

result = strcat(s1, (const char*)s2[3]); // application crashes here

The second argument of strcat() is a const char *. You are
passing a character. The cast to const char * is not going to
help.

You will have to construct a real string:

Oh, you don't have to create a temp.
size_t len;

len = strlen (s1);

s1[len] = s2[3];

s1[len+1] = 0;

As long as there is room to expand, of course.


Brian Rodenborn

[Ben Pfaff]

Default User <fi********@company.com> writes:

Ben Pfaff wrote:

Sona <so**********@nospam.com> writes:

...

result = strcat(s1, (const char*)s2[3]); // application crashes here

The second argument of strcat() is a const char *. You are
passing a character. The cast to const char * is not going to
help.

You will have to construct a real string:

Oh, you don't have to create a temp.

Presumably the OP wanted to use strcat().
--
int main(void){char p[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv wxyz.\
\n",*q="kl BIcNBFr.NKEzjwCIxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+=strchr(p,*q++)-p;if(i>=(int)sizeof p)i-=sizeof p-1;putchar(p[i]\
);}return 0;}

[Ben Pfaff]

Ben Pfaff <bl*@cs.stanford.edu> writes:

Default User <fi********@company.com> writes:

Ben Pfaff wrote:

Sona <so**********@nospam.com> writes:

...

> result = strcat(s1, (const char*)s2[3]); // application crashes here

The second argument of strcat() is a const char *. You are
passing a character. The cast to const char * is not going to
help.

You will have to construct a real string:

Oh, you don't have to create a temp.

Presumably the OP wanted to use strcat().

If not, here's an "easy" way:
sprintf(strchr(s1, '\0'), "%c", s2[3]);
--
"...Almost makes you wonder why Heisenberg didn't include postinc/dec operators
in the uncertainty principle. Which of course makes the above equivalent to
Schrodinger's pointer..."
--Anthony McDonald

[Steve Zimmerman]

Sona wrote:

Hi,

How is it possible to convert a char to char* in C? I'm trying to append
a char to the end of a char* using the strcat function.. the following
however is not working:

char* s1, *s2;
char* result;
...

...
result = strcat(s1, (const char*)s2[3]); // application crashes here

What am I doing wrong? thanks

Sona

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

int main()
{
char str1[] = "Your grade is ";
char str2[] = "A";

char str3[1];

strcpy(str3, strcat(str1, str2));

printf("%s\n", str3);

return 0;
}

--Steve

[Irrwahn Grausewitz]

Steve Zimmerman <st******@sonic.net> wrote:
<SNIP>

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

int main()
{
char str1[] = "Your grade is ";
char str2[] = "A";

char str3[1];

strcpy(str3, strcat(str1, str2));

BOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOM - - -
dangelangelangdingplong...

You know what's caused the UB, don't you?

<SNIP>

--
Computer: a million morons working at the speed of light.

[Tom Zych]

Steve Zimmerman wrote:

int main()
{
char str1[] = "Your grade is ";
char str2[] = "A";

char str3[1];

strcpy(str3, strcat(str1, str2));

printf("%s\n", str3);

return 0;
}

strcat changes dest in place. str1 can't be changed. str3 is only
one byte long.

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

[Joe Wright]

Tom Zych wrote:

Steve Zimmerman wrote:

int main()
{
char str1[] = "Your grade is ";
char str2[] = "A";

char str3[1];

strcpy(str3, strcat(str1, str2));

printf("%s\n", str3);

return 0;
}

strcat changes dest in place. str1 can't be changed. str3 is only
one byte long.

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

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

int main(void) {
char line[100];
char *s1 = "Happy Day";
char c = 's';
strcpy(line,s1);
strncat(line, &c, 1);
printf("%s\n", line);
return 0;
}

--
Joe Wright mailto:jo********@earthlink.net
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Tom Zych]

Joe Wright wrote:

strncat(line, &c, 1);

Sweet hack!

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

[Irrwahn Grausewitz]

Tom Zych <tz******@pobox.com> wrote:

Joe Wright wrote:

strncat(line, &c, 1);

Sweet hack!

Bitter-sweet, IMHO...
Irrwahn
--
What does this red button do?

[Joe Wright]

Tom Zych wrote:

Joe Wright wrote:

strncat(line, &c, 1);

Sweet hack!

Glad you liked it.
--
Joe Wright mailto:jo********@earthlink.net
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Tom Zych]

Irrwahn Grausewitz wrote:

Tom Zych <tz******@pobox.com> wrote:

Sweet hack!

Bitter-sweet, IMHO...

?

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

[Irrwahn Grausewitz]

Tom Zych <tz******@pobox.com> wrote:

Irrwahn Grausewitz wrote:

Tom Zych <tz******@pobox.com> wrote:

>Sweet hack!

Bitter-sweet, IMHO...

?

Well, if I would encounter a similar construct in production
code I would be in serious need of vacation afterwards (in fact,
this is the case anyway, but that's not the point :-) ).

To be serious: at least I do not consider it to be particular
good style to feed a pointer to a single character to /any/
of C's string processing functions. I'm not even sure if
something like

char c = 's';
strncat( line, &c, 1 );

will not invoke undefined behaviour. Why? Well, AFAIK the
standard does not impose any restrictions on how strncat()
has to handle its second argument. If, just for example,
an implementation choses to perform a strlen() on the second
argument, for whatever reason or purpose, you are doomed.

A much better choice would be memcpy(), IMHO.

Irrwahn
--
What does this red button do?

[Martin Dickopp]

Irrwahn Grausewitz <ir*****@freenet.de> writes:

I'm not even sure if something like

char c = 's';
strncat( line, &c, 1 );

will not invoke undefined behaviour. Why? Well, AFAIK the
standard does not impose any restrictions on how strncat()
has to handle its second argument. If, just for example,
an implementation choses to perform a strlen() on the second
argument, for whatever reason or purpose, you are doomed.

The standard explicitly refers to the second argument as a pointer to an
array, and not a pointer to a string as in the case of the first argument.
It is therefore my understanding that the second argument is not required
to be a pointer to a string.

Martin

[Irrwahn Grausewitz]

Martin Dickopp <ex*************@zero-based.org> wrote:

Irrwahn Grausewitz <ir*****@freenet.de> writes:

I'm not even sure if something like

char c = 's';
strncat( line, &c, 1 );

will not invoke undefined behaviour. Why? Well, AFAIK the
standard does not impose any restrictions on how strncat()
has to handle its second argument. If, just for example,
an implementation choses to perform a strlen() on the second
argument, for whatever reason or purpose, you are doomed.

The standard explicitly refers to the second argument as a pointer to an
array, and not a pointer to a string as in the case of the first argument.
It is therefore my understanding that the second argument is not required
to be a pointer to a string.

Now, that's interesting. I have still so much to learn about C,
I'll need another two or three lifetimes to get a grip on it.
Sigh...

--
What does this red button do?

[goose]

Irrwahn Grausewitz <ir*****@freenet.de> wrote in message news:<jq********************************@4ax.com>. ..

<snipped>

of C's string processing functions. I'm not even sure if
something like

char c = 's';
strncat( line, &c, 1 );

will not invoke undefined behaviour.
it wont.
Why? Well, AFAIK the
standard does not impose any restrictions on how strncat()
has to handle its second argument. If, just for example,
an implementation choses to perform a strlen() on the second
argument, for whatever reason or purpose, you are doomed.
but the standard *does* say that the second argument is an array,
not necessarily a c-string. therefore the implementation has not
got any right to be using the second argument as a string.

A much better choice would be memcpy(), IMHO.

for a single char ? just assign poke the value into the string.

line_length = strlen (line);
line [line_length] = c;
line [line_length +1] = '\0';

its more code (2 extra lines) but is relatively clear.
goose,
hand

[Default User]

Joe Wright wrote:

Tom Zych wrote:

Joe Wright wrote:

strncat(line, &c, 1);

Sweet hack!

Glad you liked it.

Using a function call of any sort where a simple array insert takes care
of the problem seems somewhat overdone.


Brian Rodenborn

[Default User]

Ben Pfaff wrote:

Default User <fi********@company.com> writes:

Oh, you don't have to create a temp.

Presumably the OP wanted to use strcat().

Well, as it is obvious that the OP didn't know what to do, it's best to
try to show the correct way not the one closest in-line with the failed
attempt.


Brian Rodenborn

[Tom Zych]

Default User wrote:

> strncat(line, &c, 1);

Using a function call of any sort where a simple array insert takes care
of the problem seems somewhat overdone.

The array insert wouldn't be so simple. You have to use strlen to
find the right place. Then you have to copy c. Then you have to
terminate line again. This one call does all that.

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

[Default User]

Tom Zych wrote:

Default User wrote:

> > strncat(line, &c, 1);

Using a function call of any sort where a simple array insert takes care
of the problem seems somewhat overdone.

The array insert wouldn't be so simple. You have to use strlen to
find the right place. Then you have to copy c. Then you have to
terminate line again. This one call does all that.

Perhaps so.


Brian Rodenborn

[Jack Klein]

On Wed, 10 Sep 2003 15:13:46 GMT, Joe Wright
<jo********@earthlink.net> wrote in comp.lang.c:

Tom Zych wrote:

Steve Zimmerman wrote:

int main()
{
char str1[] = "Your grade is ";
char str2[] = "A";

char str3[1];

strcpy(str3, strcat(str1, str2));

printf("%s\n", str3);

return 0;
}

strcat changes dest in place. str1 can't be changed. str3 is only
one byte long.

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

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

int main(void) {
char line[100];
char *s1 = "Happy Day";
char c = 's';
strcpy(line,s1);
strncat(line, &c, 1);
printf("%s\n", line);
return 0;
}

Undefined behavior.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq

[Jack Klein]

On Fri, 12 Sep 2003 02:04:15 GMT, Jack Klein <ja*******@spamcop.net>
wrote in comp.lang.c:

On Wed, 10 Sep 2003 15:13:46 GMT, Joe Wright
<jo********@earthlink.net> wrote in comp.lang.c:

Tom Zych wrote:

Steve Zimmerman wrote:

> int main()
> {
> char str1[] = "Your grade is ";
> char str2[] = "A";
>
> char str3[1];
>
> strcpy(str3, strcat(str1, str2));
>
> printf("%s\n", str3);
>
> return 0;
> }

strcat changes dest in place. str1 can't be changed. str3 is only
one byte long.

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

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

int main(void) {
char line[100];
char *s1 = "Happy Day";
char c = 's';
strcpy(line,s1);
strncat(line, &c, 1);
printf("%s\n", line);
return 0;
}

Undefined behavior.

Sorry, my bad, no it's not.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq