Get scanf to quit when it reads a newline?

Use fgets to read console input: int res = 2; while (res == 2) { char buf100; fgets(buf, sizeof(buf), stdin); res = sscanf(buf, "%f %f", &real, &img); if (res == 2) ci++ = real + img * I; } ci++ = 1 + 0*I; // most significant coefficient is assumed to be 1 return i.

Giving you the credit since you mentioned fgets and sscanf first. – Matt Sep 16 '10 at 1:34 Thanks, just realised c probably won't let you declare the buffer inside the while loop but the concept is there. – MattSmith Sep 16 '10 at 1:45 That declaration is perfectly fine.

– jamesdlin Sep 16 '10 at 5:59.

The specific problem you're having is that a scanf format string of %f will skip white space (including newlines) until it finds an actual character to scan. From the c99 standard: A conversion specification is executed in the following steps: - Input white-space characters (as specified by the isspace function) are skipped, unless the specification includes a '', 'c', or 'n' specifier. And, elsewhere, describing isspace(): The standard white-space characters are the following: space ' ', form feed '\f', new-line '\n', carriage return '\r', horizontal tab '\t', and vertical tab '\v'.

Your best bet is to use fgets to get the line (and this can be protected from buffer overflow very easily), then use sscanf on the resultant line. The scanf function is one of those ones you should look at very warily. The following piece of code is one I often use to handle line input: #include #include #define OK 0 #define NO_INPUT 1 #define TOO_LONG 2 static int getLine (char *prmpt, char *buff, size_t sz) { int ch, extra; // Get line with buffer overrun protection.

If (prmpt! = NULL) { printf ("%s", prmpt); fflush (stdout); } if (fgets (buff, sz, stdin) == NULL) return NO_INPUT; // If it was too long, there'll be no newline. In that case, we flush // to end of line so that excess doesn't affect the next call.

If (buffstrlen(buff)-1! = '\n') { extra = 0; while (((ch = getchar())! = '\n') && (ch!

= EOF)) extra = 1; return (extra == 1)? TOO_LONG : OK; } // Otherwise remove newline and give string back to caller. Buffstrlen(buff)-1 = '\0'; return OK; } // Test program for getLine().

Int main (void) { int rc; char buff10; rc = getLine ("Enter string> ", buff, sizeof(buff)); if (rc == NO_INPUT) { // Extra NL since my system doesn't output that on EOF. Printf ("\nNo input\n"); return 1; } if (rc == TOO_LONG) { printf ("Input too long %s\n", buff); return 1; } printf ("OK %s\n", buff); return 0; } Testing it with various combinations: pax> . /prog Enter string>CTRL-D No input pax> .

/prog Enter string> a OK a pax> . /prog Enter string> hello OK hello pax> . /prog Enter string> hello there Input too long hello the pax> .

/prog Enter string> I am pax OK I am pax What I would do is to use this function to get a line safely, then simply use: sscanf (buffer, "%f %f", &real, &img) to get the actual values (and check the count). In fact, here's a complete program which is closer to what you want: #include #include #define OK 0 #define NO_INPUT 1 #define TOO_LONG 2 static int getLine (char *prmpt, char *buff, size_t sz) { int ch, extra; // Get line with buffer overrun protection. If (prmpt!

= NULL) { printf ("%s", prmpt); fflush (stdout); } if (fgets (buff, sz, stdin) == NULL) return NO_INPUT; // If it was too long, there'll be no newline. In that case, we flush // to end of line so that excess doesn't affect the next call. If (buffstrlen(buff)-1!

= '\n') { extra = 0; while (((ch = getchar())! = '\n') && (ch! = EOF)) extra = 1; return (extra == 1)?

TOO_LONG : OK; } // Otherwise remove newline and give string back to caller. Buffstrlen(buff)-1 = '\0'; return OK; } int main (void) { int I = 1, rc; char prompt50, buff50; float real, imag; while (1) { sprintf (prompt, "\nEnter real and imaginary for #%3d: ", i); rc = getLine (prompt, buff, sizeof(buff)); if (rc == NO_INPUT) break; if (*buff == '\0') break; if (rc == TOO_LONG) { printf ("** Input too long %s...\n", buff); } if (sscanf (buff, "%f %f", &real, &imag) == 2) { printf ("Values were %f and %f\n", real, imag); i++; } else { printf ("** Invalid input %s\n", buff); } } return 0; } along with a test run: pax> . /testprog Enter real and imaginary for # 1: hello ** Invalid input hello Enter real and imaginary for # 1: hello there ** Invalid input hello there Enter real and imaginary for # 1: 1 ** Invalid input 1 Enter real and imaginary for # 1: 1.23 4.56 Values were 1.230000 and 4.560000 Enter real and imaginary for # 2: pax.

1 Using scanf to read input from the user often introduces problems like this. It is usually much less error-prone to simply read the input as a string and then parse the string. – bta Sep 16 '10 at 1:32.

There's a way to do what you want using just scanf: int readCoefficents(double complex *c) { int I = 0; double real; double img; char buf2; while (scanf("%1\n", buf) == 0) { // loop until a blank line or EOF if (scanf("%lf %lf", &real, &img) == 2) // read two floats ci++ = real + img * I; scanf("%*^\n"); // skip the rest of the line scanf("%*1\n"); // and the newline } ci++ = 1 + 0*I; // most significant coefficient is assumed to be 1 return i; } If the user only enters 1 float on a line, it will read the next line for the second value. If any random garbage is entered, it will skip up to a newline and try again with the next line. Otherwise, it will just go on reading pairs of float values until the user enters a blank line or an EOF is reached.

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