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cstringfilefgets

Can C's fgets be coaxed to work with a string *not* from a file?

Specifically, the code sample here works great, but only when the string is stored in a file.

Sometimes I need it to process a generated string (stored in a string variable), but I'm having trouble convincing fgets's third parameter to work with string variables because it's a pointer to a FILE structure.

Or perhaps there's a functional equivalent to fgets that may be used on strings?

Any suggestions? Thanks!

Solution

  • In the spirit of hacking together quick answers, here is "sgets" that I just wrote. It attempts to emulate fgets but with string input.

    Edit Fixed a bug that Monte pointed out (thanks). Madly typing out a utility while believing that at least 15 other people with the exact same idea are frantically doing the same thing does not lead to well-tested code. Bad me. The original version was including the newline character on the succeeding call.

    char *sgets( char * str, int num, char **input )
{
    char *next = *input;
    int  numread = 0;

    while ( numread + 1 < num && *next ) {
        int isnewline = ( *next == '\n' );
        *str++ = *next++;
        numread++;
        // newline terminates the line but is included
        if ( isnewline )
            break;
    }

    if ( numread == 0 )
        return NULL;  // "eof"

    // must have hit the null terminator or end of line
    *str = '\0';  // null terminate this tring
    // set up input for next call
    *input = next;
    return str;
}


int main( int argc, char* argv[] )
{
    // quick and dirty test
    char *str = "abc\ndefghitjklksd\na\n12345\n12345\n123456\nabc\n\n";
    char buf[5];

    while ( sgets( buf, sizeof( buf ), &str ))
        printf( "'%s'\n", buf );
}