Thread: how do I combine two strings together

Are you talking about attaching one string to another?

if so, then:

Code:

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

main()
 {
   char str_output[20]={0}, str_two[]="two";

   strcpy(str_output, "one");       // copies "one" into str_output
   strcat(str_output, str_two);    //  attaches str_two to str_output

   printf("The Output string is: %s", str_output);
 }

/*program to concat without using strcpy and strcat functions */
#include<stdio.h>
#include<string.h>
main()
{char a[]="hello world"; /*ur 1st string goes here*/
char b[]="how are you"; /*sencond string goes here*/
func1(b,a);
getchar();
}
func1(char *b,char *a)
{
int k,j;
k=strlen(a);
for(j=0;j<=strlen(b);j++)
{a[k+1]=b[j];
k++;
}
for(j=0;j<=((strlen(a)));j++)
printf("%c",a[j]);
}

You've been here for 20 posts so far, and you still are too lazy to actually use code tags. You'll want to correct that.

Quzah.

Also, main() is no longer valid C.

Code:

//program to Combine Two Strings  Using Pointers 
#include<stdio.h>
#include<conio.h>
main()
{
void combine(char*,char*,char*);
char *a="",*b="Hello",*c="World";
combine(a,b,c);printf("Combined String Is %s",a);
getch();return 0;
}

void combine(char *res,char *str1,char *str2)
{
while(*str1!='\0')
*res++=*str1++;
while(*str2!='\0')
*res++=*str2++;
*res='\0';
}

Originally posted by Speedy5
Or maybe use the new operator to allocate some memory and delete it later. There is no reason at all to not use the strcat() functions as described above.

Wrong forum. C has no 'new' and 'delete' operators.

Quzah.

Lolzzzzz
it does work when simply you access members
of any array using address operator particularly
in your own functions of void type but if you use
strcpy strcat or such any other function to deal with strings and arrays in your self made function it will certainly not work, in that case you will have to return some
value or to assign it so some variable
I dont know why it is so but it work correctly even if u dont
return any value it will assign returning value to first comment
of that void type function.
if u dont agree with it just compile it with ur TC Compiler and then post ur reply

Originally posted by Rose_Flowers
Lolzzzzz
it does work when simply you access members
of any array using address operator particularly

Please actually know what you're talking about here. Granted, I tend to stick my foot in my mouth from time to time, but I usually recognize when I'm wrong.

You cannot overrun your array boundaries without adverse side effects. Maybe not now, maybe not visible to you, but it is wrong.

Furthermore, you cannot modify string literals.

It is flat out wrong to modify data you have not implicitly allocated. Yes, your compiler will let you make a pointer point to any memory space you want. Yes, you can try to blindly write data to that location. No, it is not correct. It is wrong. It will crash your program, or some one else's program, but it is wrong. End of discussion.

Learn how to correctly access and allocate memory, or don't use pointers.

Quzah.

Originally posted by P.Phant
Sorry I'm kind of highjacking the thread but I've been wondering about this for some time:

say I write
foo1("Hello World");
and somewhere else in the same module:
foo2("Hello World");

Will the compiler optimize those two calls to pass the same address, only writting "Hello World" once in the assembly code?

Most likely, yes. My understanding of it is that it builds a string table which it stores all string literals in. Any identical string will most likely just be treated as the same entry.

In MSVC++, with no optimizations, here's what I get from the following code example:

Code:

#include <stdio.h>

char * foostr = "Hello World";

int main( void )
{
    char *foostr2 = "Hello World";

    printf("%p, %p\n", foostr, foostr2 );
    return 0;
}

/*
    Output:
    0042001c, 0042001c
*/

When in doubt, try it out.

[edit]
I modified printf to use %p instead of %x so it's "more correct" from a learning point of view. :P (Though the end result is really the same.)

So to answer your final question, yes, this really is the reason you can't modify string literals. Because they're optimized into a string table which would basicly break it if you modified one of the "Hello World" strings some place.
[/edit]

Quzah.

Originally posted by Salem
> if u dont agree with it just compile it with ur TC Compiler and then post ur reply
Not everyone uses a fossil compiler on a broken OS which lets you spray data all over memory without a care in the world.

It ain't broken, it works exactly as designed And it does care, is just doesn't BSOD

Code:

//program to Combine Two Strings  Using Pointers 
#include<stdio.h>
main()
{
    void combine(char *, char *, char *);
    char *a = NULL, *b = "Hello", *c = "World";
    combine(a, b, c);
    printf("Combined String Is %s", a);
    return 0;
}

Oh, and before you spout about how you just had char *a, remember that you were pointing at a random memory location, which would be randomly used by something else. The fact that your TC compiled program didn't crash was luck.

Well, not really random -- it points to the exact spot that the "Divide by Zero" interrupt address is...

Originally posted by P.Phant
Will the compiler optimize those two calls to pass the same address, only writting "Hello World" once in the assembly code?

It may or may not.

ISO/IEC 9899:1999 (E): 6.5.2.5p8 String literals, and compound literals with const-qualified types, need not designate distinct objects.82)
82) This allows implementations to share storage for string literals and constant compound literals with the same or overlapping representations.

I'm not sure about C90.

Code:

#include <stdio.h>

void foo(const char *s)
{
   printf("%p \"%s\"\n", s, s);
}

int main(void)
{
   foo("Hello world");
   foo("Hello world");
   return 0;
}

/* Borland C++ 5.0 for Win32 / Microsoft Windows 2000 [Version 5.00.2195]
0040A131 "Hello world"
0040A13D "Hello world"
*/

And my output for Quzah's code was this.

Code:

00407078, 00407084