How to use strcat in c?

Hi,
Today I decided to code a small program that could make a backup file.
I wanted to change the extension of the given file to "BAK" to be able
to make a backup file.

So I coded the below program but when I tried to use strcat(); function
to change the extension of the given file to a backup file I faced a problem
and I was not able to handle it.

Finally after pondering a lot,I changed my program and used a for loop
to be able to solve the problem.
You can see this loop in the second program which is below.
But it was not what i wanted to do.
I wanted to use strcat(); function and I hope someone can help me
to correct the first program.

Thanks in advance.
Best Regards,
Zest.

The imcomplete program:

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

#define SIZE 40
int main(int argc,char * argv[])
{
	FILE *in,*out;
	char name[SIZE],chr = '.',bk[] = "Bak",ch;
	char *occurance;


	if(argc != 2)
	{
		puts("This program makes a BackUp of your files");
		fprintf(stderr,"Usage: %s filename\n",argv[0]);
		exit(EXIT_FAILURE);
		}
		if((in = fopen(argv[1],"r")) == NULL)
		{
			fprintf(stderr,"I can't open the file %s",argv[1]);
			exit(EXIT_FAILURE);
			}


			strncpy(name,argv[1],SIZE-5);
			name[SIZE-5] = '\0';

			occurance = strchr(name,chr);

			strcat(occurance , bk);

			if((out = fopen(name, "w")) == NULL)
			{
				fprintf(stderr,"I can't copy to the file %s",name);
				exit(EXIT_FAILURE);
				}

				//Copying Data

				while((ch = getc(in))!= EOF)
				putc(ch,out);
				
				if(fclose(in) != 0 || fclose(out) != 0)
				fprintf(stderr,"Error is closing files.\n");

				puts("Done!\n");



				getch();
				return 0;

				}

The program with for loop:

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

#define SIZE 40
int main(int argc, char* argv[])
{	
	FILE *in,*out;
	char name[SIZE],chr = '.',bk[] = ".Bak",ch;
	char *occurance;


	if(argc != 2)
	{
		puts("This program makes a BackUp of your files");
		fprintf(stderr,"Usage: %s filename\n",argv[0]);
		exit(EXIT_FAILURE);
		}
		if((in = fopen(argv[1],"r")) == NULL)
		{
			fprintf(stderr,"I can't open the file %s",argv[1]);
			exit(EXIT_FAILURE);
			}


			strncpy(name,argv[1],SIZE-5);
			name[SIZE-5] = '\0';

			occurance = strchr(name,chr);
			
			for(int i = 0; i < 4; i++)
			   *(occurance + i) = bk[i];

			

			if((out = fopen(name, "w")) == NULL)
			{
				fprintf(stderr,"I can't copy to the file %s",name);
				exit(EXIT_FAILURE);
				}

				//Copying Data
				
				while((ch = getc(in))!= EOF)
				putc(ch,out);

				if(fclose(in) != 0 || fclose(out) != 0)
				fprintf(stderr,"Error is closing files.\n");

				puts("Done!\n");



				getch();
				return 0;

				}

[piccolo]

Now why would you want to use strcat?? This routine you have now is quite slow reading on a character base is too slow. Use fread and fwrite.

strcat useage is as follows:
...
char dest[20];

dest[0]='\';
strcat(dest,"this is a ");
//now dest="this is a\0"
strcat(dest,"test");
//now dest="this is a test\0"
strcat(dest,"123456789012345678901234567890");
//now you get a crash because your dest string overflows, so this is a buffer overflow.

Easier loop:
char buffer[1024];
...
while !feof(in){
nrbytes=fread(buffer,1,1024,in);
if (nrbytes) fwrite(buffer,1,nrbytes,out);
}
etc..
Backupping files can be done faster using windows functions if yer running windoze.

[leosmi05]

Just some small remarks regarding your program.
It seems that it can not handle well an extension of 1 or 2 characters or more than 3 characters.
You should start from the back of the file name (argv[1]) and search for the last point '.' character.

And BTW, you don't need to use strcat in case you have at least 3 characters for extension. Just find the last '.' in the name and replace the next 4 characters with "BAK" and '\0'.

The other remarks from piccolo also remain.

Don't know if it's useful for you, but you could use the API PathRenameExtension , which is in shlwapi.dll, this API replace any extension with any extension you want:

PathRenameExtension ("file.ext", ".bak");

Hope it works for you, just #include <shlwapi.h>

This only works in windows, off course...

Here is a generalized routine good for your situation
and can be easily tailored or adapted to fit most
any situation:

// EX: OPEN A FILE FOR LOGGING OUTPUT IN ANALYZE MODE.
// Find the last '\\' to obtain a pointer to just the base file name part if
your buffer contains any path type info
// We could just as eaily searched for last '.' to obtain base file name
extension pointer.

char *szBuffer = buffer;
PCSTR pszBaseName = strrchr( szBuffer, '\\' );
if ( pszBaseName )  // We found a '\\', so advance to the base FILE name
{
// Increment 1 byte past our pointer
pszBaseName++;
strncpy(pszBaseName, "Asprlog.txt\0", 12); // we need 12 to include '\0'
null char	
//replace base file name with newname , here you could have appended
bak or BAK extension if you had searched on the '.' char Ex: as so: 
strncpy(pszBaseName, "bak\0", 4);
}
FILE * pFile;
pFile=fopen(szBuffer,"wt");	// open for write

... and so on, I hope you get the idea.

cheers!

maybe you could try the following routine to search for the '.' from the end of the filename:

char Filename[]= "c:\\path\\file.ext";
char *BaseFileName;
strrev(Filename);
BaseFileName = strstr(Filename,"."); // search for the '.'
if (BaseFileName){ 
    BaseFileName = (char*)(BaseFileName+1); // exclude the '.'
    strcpy(Filename,BaseFileName);
}
strrev(Filename);
strcat(Filename,".bak\0");

this should work even if the filename does not include a full path
well of course there are still a bunch of ways to implement this.

anyways, hope this helps...

well of course there are still a bunch of ways to implement this.

yes you can try

fnsplit() , fnmerge() i think its in dir.h

splitpath() , makepath() defined in stdlib.h

these all take care to find . on thier own
all you need to give is buffers for specific paths
and then just switch what you dont with what you need and compose back

Dear condzero,
Hi,
Thanks for your help and reply.
But there is still a problem for me that I couldn't manage it.
Would you please let me know how to OPEN A FILE FOR LOGGING OUTPUT IN ANALYZE MODE?
Which function(s) do you use to OPEN A FILE FOR LOGGING OUTPUT IN ANALYZE MODE?
That would be great if you can discuss the case a bit.
I look forward to hearing from you.

Also thank anybody else who has spend time to answer to this topic to bring some help to the point.

Regards,
Zest.

Hi Zest,

Not sure what you mean by "Analyze Mode".

In my example, I open a file with the parameter "wt" (Write, text mode).
Then I simply create my output:

char b[1024];
unsigned    int o = 0;		//Loop counter
FILE * pFile;
pFile=fopen("myfile.txt","wt");	// open for write text mode

// Use a loop and print your output, or just keep appending data to a buffer
then print the entire buffer (Note: Use of new line char n)
LOOP:
sprintf( b, "Some text\n")
fputs (b,pFile);   // or possibly fwrite (b , 1 , 80 , pFile); (where 80 is the
length of your text, not sure which way is more applicable as I generally
use the code below)
...

//or
for ( o = 0; o < strlen(b); o++ )
{
putc(b[o], pFile);
}

// CLOSE THE FILE.
fclose (pFile);

This produces a nice clean text file.

Perhaps others can elaborate more.

cheers.