Strtod: Difference between revisions
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#redirect [[C miscellaneous operations#Function overview]] |
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{{lowercase|strtod}} |
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{{merge to|C string|discuss=Talk:C_standard_library#Pages_for_each_function_and_WP:NOTMANUAL|date=October 2011}} |
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'''strtod''' ('''''str'''ing '''to d'''ouble'') is a [[C (programming language)|C language]] function that converts a character [[text string|string]] to a [[double precision]] [[floating-point]] value<ref>{{cite book |
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| url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf |
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| title=ISO/IEC 9899:1999 specification |
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| at=p. 308, § 7.20.1.3 |
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}}</ref>. It is defined as: |
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:<code>double strtod ( const char * str, char ** endptr );</code> |
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==Overview== |
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The strtod function parses the C string str interpreting its content as a floating point number and returns its value as a double. If endptr is not a null pointer, the function also sets the value pointed by endptr to point to the first character after the number. |
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The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes as many characters as possible that are valid following a syntax resembling that of floating point literals, and interprets them as a numerical value. A pointer to the rest of the string after the last valid character is stored in the object pointed by endptr. |
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A valid floating point number for strtod is formed by a succession of: |
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* An optional plus or minus sign |
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* A sequence of digits, optionally containing a decimal-point character |
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* An optional exponent part, which itself consists on an 'e' or 'E' character followed by an optional sign and a sequence of digits. |
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If the first sequence of non-whitespace characters in str does not form a valid floating-point number as just defined, or if no such sequence exists because either str is empty or contains only whitespace characters, no conversion is performed. |
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==Parameters== |
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str |
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* C string beginning with the representation of a floating-point number. |
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endptr |
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* Reference to an already allocated object of type char*, whose value is set by the function to the next character in str after the numerical value. This parameter can also be a null pointer, in which case it is not used. |
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==Return value== |
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On success, the function returns the converted floating point number as a double value. |
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If no valid conversion could be performed, a zero value (0.0) is returned. |
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If the correct value is out of the range of representable values, a positive or negative HUGE_VAL is returned, and the global variable errno is set to ERANGE. |
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If the correct value would cause underflow, zero is returned and errno is set to ERANGE. |
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The strtod function is included in the [[stdlib.h]] header file of the ISO/IEC standard C [[library (computing)|library]]. |
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==See also== |
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{{col-begin}} |
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{{col-break|width=33%}} |
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*[[ASCII]] |
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*[[atoi]] |
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*[[atof]] |
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*[[C (programming language)]] |
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*[[C++]] |
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{{col-break}} |
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*[[Floating point]] |
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*[[Double precision]] |
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*[[Quadruple precision]] |
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*[[stdlib.h]] |
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*[[strtol]] |
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{{col-end}} |
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==References== |
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{{reflist}} |
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==External links== |
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* [http://en.cppreference.com/w/cpp/string/narrow/strtod C++ reference for <code>std::strtod</code>] |
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[[Category:C standard library]] |
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[[Category:stdlib.h]] |
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[[ru:Strtod]] |
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Revision as of 22:39, 31 October 2011
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