National Instruments 320682C

Chapter 2 Formatting and I/O Library

When locating a real number in a string, Scan skips over white space characters. If a non-

numeric character other than a white space character, +, or - is found before the first numeric

character, the Scan call fails. Thus, Scan fails on the p in p12.3; it leaves the value in x

unmodified and returns zero, indicating that no target specifiers were satisfied.

s = "12.3m";

n = Scan (s, "%s>%f", &x); /* result: x = 12.3, n = 1 */

s = "12.3.4";

n = Scan (s, "%s>%f", &x); /* result: x = 12.3, n = 1 */

s = "1.23e";

n = Scan (s, "%s>%f", &x); /* result: x = ????, n = 0 */

Scan considers the occurrence of a non-numeric character (such as the m in 12.3m) to mark the

end of the real number. A second decimal point also marks the end of the number. However,

Scan fails on "1.23e" because the value of the exponent is missing.

s = "1.2345";

n = Scan (s, "%s>%f[w4]", &x);/* result: x = 1.23, n = 1 */

The w4 modifier specifies that only the first 4 bytes of the string are scanned.

String to Integer and Real

char *s;

int a, n;

double x;

s = "32 1.23";

n = Scan (s, "%s>%i%f", &a, &x);

/* result: a = 32, x = 1.23, n = 2 */

s = "32, 1.23";

n = Scan (s, "%s>%i[x]%f", &a, &x);

/* result: a = 32, x = 1.23, n = 2 */

s = "32, 1.23";

n = Scan (s, "%s>%i%f", &a, &x);

/* result: a = 32, x = ????, n = 1 */

Remarks

After each of the first two calls to Scan, a = 32, x = 1.23, and n = 2 (indicating that two target

specifiers were satisfied). In the second call, the x modifier is used to discard the separating

comma.

In the third call, there is a comma separator after the integer, but the x modifier is absent.

Consequently, Scan fails when attempting to find the real number. x remains unmodified, and

n = 1 (indicating that only one target specifier was satisfied).