Read from stdin using read

Question

I'm using the following code to read from stdin

int size;
int bufferSize=2000;
char echoString[bufferSize];
while ((size = read(fileno(stdin), echoString, bufferSize)) > 0){
 write(fileno(stdout), echoString, size);
}

To write the data got from stdin on the screen... but it just dont work well. If i do a cat "hugetarfile.tar.gz" | ./myprogram | tar -zvt it works, but on the end it "crashed" telling there are some trash. If i do cat "hugetarfile.tar.gz" | tar -zvt it works like a charm..

on the end of the tar you can see:

gzip: stdin: decompression OK, trailing garbage ignored tar: Child returned status 2 added the File *fin = freopen(nill, "rb", "stdin")

Someone can help me? xD

Just to tell... i'm creating the read to send trough socket, but in this case this war is easier to test.

Answer 1

I completed your program in the simplest way to make it compile without warning with gcc -ansi -D_POSIX_C_SOURCE -Wall -W demonofnight.c:

#include <unistd.h>
#include <stdio.h>

int main()
{
    int size;
    int const bufferSize=2000;
    char echoString[bufferSize];
    while ((size = read(fileno(stdin), echoString, bufferSize)) > 0){
        write(fileno(stdout), echoString, size);
    }
    return 0;
}

and executed it with

cat bigFile | ./a.out | md5sum

for several big files. I got the same md5 than with md5sum bigFile.

Conclusion: the error is in what you don't show us.

Answer 2

You must test for errors in your read and write. Why don't you test your program like:

./myprogram < hugetarfile.tar.gz > output.tar.gz  

and make sure that hugetarfile.tar.gz and output.tar.gz are the same.

Regards