National Instruments 320682C

Chapter 2 Formatting and I/O Library

String to Integer and String

char *s;

char buf[10];

int a, n;

s = "32abc";

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

/* result: a = 32, buf = "abc", n = 2 */

s = "32abc";

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

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

Remarks

After the first call to Scan, a = 32, buf = "abc", and n = 2. Notice there are no spaces in the

format string between the two target specifiers. In the second call, there is a space between %i

and %s. Consequently, Scan expects a space to occur in s immediately after the integer.

Because there is no space in s, Scan fails at that point. It leaves buf unmodified and returns 1

(indicating that only one target specifier is satisfied).

Note: Do not put spaces between specifiers in Scan, ScanFile, or ScanIn format strings.

String to Real, Skipping over Non-Numeric Characters in the String

char *s;

double x;

int n;

s = "VOLTS = 1.2";

n = Scan (s, "%s>%s[dt#]%f", &x); /* result: x = 1.2, n = 2 */

s = "VOLTS = 1.2";

n = Scan (s, "%s[i8]>%f", &x); /* result: x = 1.2, n = 1 */

s = "VOLTS = 1.2";

n = Scan (s, "%s>VOLTS = %f", &x); /* result: x = 1.2, n = 1 */

Remarks

The three different format strings represent different methods for skipping over non-numeric

characters. In the first call, the format string contains two target specifiers. In the first specifier

(%s[dt#]), the t# modifier instructs Scan to read bytes from s until a number is

encountered. The d modifier indicates that the bytes must be discarded because there is no

argument corresponding to the specifier. When the Scan call succeeds, it returns 2, indicating

that two target specifiers were satisfied, even though there is only one target argument.

In the second call, the source specifier %s[i8] instructs Scan to ignore the first 8 bytes of s.

This method works only if the location of the number within s is always the same.

In the third call, the format string contains the non-numeric characters literally. This method

works only if the non-numeric characters in s are always the same.