CODEWITHSUNDEEP
clinuxmacospipe
gino gino
gino gino

Reputation: 269

reading Named Pipe issue

I have this code C:

#define BUFSIZE 256

int main ( int argc, char *argv[])
{
    int fdIn;
    int fdOut;


    if( argc != 3)
    {
        perror("Erro argument");
        exit(1);
    }

    if( (fdIn = open(argv[1], O_RDONLY ) )<0)
    {
        perror("Errr pipe input");
        exit(1);
    }

    if( (fdOut = open(argv[2], O_WRONLY ) )<0)
    {
        perror("Errr pipe output");
        exit(1);
    }

    int c = 2;
    while(c--)
    {
        char var1[BUFSIZE];
        char var2[BUFSIZE];
        char string[100];

        memset(var1, 0, sizeof(var1));
        memset(var2, 0, sizeof(var2));
        memset(string, 0, sizeof(string));


        if( readLine(fdIn, var1, sizeof(var1)) == 0)
        {
            printf("exit1\n");
            exit(0);
        }
        printf("%s\n",var1);
        if( readLine(fdIn, var2, sizeof(var2)) == 0)
        {
            printf("exit2\n");
            exit(0);
        }

        removeNewLine(var1);
        removeNewLine(var2);

        if( atoi(var2) != 0){
            if( atoi(var1) == 0  || (atoi(var1) % atoi(var2)) == 0 )
                sprintf(string,"ok\n");
            else
                sprintf(string,"no\n");

        }

        printf("%s", string);
        writeLine(fdOut, string, strlen(string));
    }
    close(fdOut);
    close(fdIn);
    exit(0);

}

Functions used in the code:

int readLine( int fd, char* str, int bufferSize)
        {
            return readToDel(fd, '\n', str, bufferSize);
        }

int readToDel( int fd, char delimiter, char* str, int bufferSize)
        {
            int n;
            int byteLetti =0;
            int index=0;

            do /* Read characters until NULL or end-of-input */
            {

                if( (n = read (fd, str+index, 1)) < 0)
                {
                    perror("Errore: lettura dal file descriptor fallita\n");
                    exit(1);
                }
                byteLetti+=n;


            }
            while (n > 0 && *(str+index++) != delimiter && index < bufferSize);


            return byteLetti; /* Return false if end-of-input */
        }
void removeNewLine( char *s )
    {
        removeDel(s, "\r\n");
    }
void removeDel( char *s, char *del)
    {
        s[strcspn ( s, del )] = '\0';
    }

I have 2 pipes one for input and other for output. I write on input pipe , using echo "4\n2\n" > i (by terminal) the string "4\n2\n" and by two readline( the 2 if in the while cycle) I should read the "4" and then by second readline the "2". This because the Readline function splits by '\n'; but when end first if in the while cycle prints var1 (should contain only "4" ) , but it prints 4\n2\n and I don't understand why. What do I wrong?

Upvotes: 1

Views: 469

Answers (1)

Ken Thomases
Ken Thomases

Reputation: 90521

\n is not actually a newline character. It's an escape sequence which, in some circumstances, is interpreted and causes the interpreter to substitute a newline character. The C compiler does this interpretation and substitution in string and character literals, so your compiled program actually contains the newline character.

The shell and its echo built-in command do not necessarily do this interpretation. The bash that ships with OS X does not interpret such escape sequences by default. You can make it do that by passing the -e option. Note that /bin/echo or the built-in echo commands of other shells may not support that option.

So, you throught you were providing the input character stream 4, newline, 2, newline, newline to your program. What you were actually providing was 4, \, n, 2, \, n, newline.

Upvotes: 1

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