From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/c/string%2Fbyte%2Fstrtof.html | 90 +++++++++++++++++++++++++++++++++++ 1 file changed, 90 insertions(+) create mode 100644 devdocs/c/string%2Fbyte%2Fstrtof.html (limited to 'devdocs/c/string%2Fbyte%2Fstrtof.html') diff --git a/devdocs/c/string%2Fbyte%2Fstrtof.html b/devdocs/c/string%2Fbyte%2Fstrtof.html new file mode 100644 index 00000000..b3be49b7 --- /dev/null +++ b/devdocs/c/string%2Fbyte%2Fstrtof.html @@ -0,0 +1,90 @@ +

strtof, strtod, strtold

Defined in header <stdlib.h> 
float       strtof( const char *restrict str, char **restrict str_end );
+		 (since C99) 
double      strtod( const char          *str, char          **str_end );
 (until C99) 
double      strtod( const char *restrict str, char **restrict str_end );
+		 (since C99) 
long double strtold( const char *restrict str, char **restrict str_end );
+		 (since C99)

Interprets a floating-point value in a byte string pointed to by str.

+

Function discards any whitespace characters (as determined by isspace) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid floating-point representation and converts them to a floating-point value. The valid floating-point value can be one of the following:

+ + +
    +
  • hexadecimal floating-point expression. It consists of the following parts:
    • +
      +
    • (optional) plus or minus sign
      • +
    • 0x or 0X
      • +
    • nonempty sequence of hexadecimal digits optionally containing a decimal-point character (as determined by the current C locale) (defines significand)
      • +
    • (optional) p or P followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 2)
      • +
    +
  • infinity expression. It consists of the following parts:
    • +
      +
    • (optional) plus or minus sign
      • +
    • INF or INFINITY ignoring case
      • +
    +
  • not-a-number expression. It consists of the following parts:
    • +
      +
    • (optional) plus or minus sign
      • +
    • NAN or NAN(char_sequence) ignoring case of the NAN part. char_sequence can only contain digits, Latin letters, and underscores. The result is a quiet NaN floating-point value.
      • +
    +
 (since C99)

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is a null pointer, it is ignored.

+

Parameters

+ + +
str - pointer to the null-terminated byte string to be interpreted
str_end - pointer to a pointer to character.

Return value

Floating-point value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs (errno is set to ERANGE) and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, ​0​ is returned.

+

Example

#include <stdio.h>
+#include <errno.h>
+#include <stdlib.h>
+ 
+int main(void)
+{
+    // parsing with error handling
+    const char *p = "111.11 -2.22 Nan nan(2) inF 0X1.BC70A3D70A3D7P+6  1.18973e+4932zzz";
+    printf("Parsing '%s':\n", p);
+    char *end;
+    for (double f = strtod(p, &end); p != end; f = strtod(p, &end))
+    {
+        printf("'%.*s' -> ", (int)(end-p), p);
+        p = end;
+        if (errno == ERANGE){
+            printf("range error, got ");
+            errno = 0;
+        }
+        printf("%f\n", f);
+    }
+ 
+    // parsing without error handling
+    printf("\"  -0.0000000123junk\"  -->  %g\n", strtod("  -0.0000000123junk", NULL));
+    printf("\"junk\"                 -->  %g\n", strtod("junk", NULL));
+}

Possible output:

+
Parsing '111.11 -2.22 Nan nan(2) inF 0X1.BC70A3D70A3D7P+6  1.18973e+4932zzz':
+'111.11' -> 111.110000
+' -2.22' -> -2.220000
+' Nan' -> nan
+' nan(2)' -> nan
+' inF' -> inf
+' 0X1.BC70A3D70A3D7P+6' -> 111.110000
+'  1.18973e+4932' -> range error, got inf
+"  -0.0000000123junk"  -->  -1.23e-08
+"junk"                 -->  0

References

See also

+ + +
converts a byte string to a floating-point value
(function)
+
(C99)(C95)(C99)
 converts a wide string to a floating-point value
(function)
C++ documentation for strtof, strtod, strtold
+

+ © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
+ https://en.cppreference.com/w/c/string/byte/strtof +

+
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