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| <h5 class="subsubsection">15.4.1.2 C and C<tt>++</tt> Constants</h5> |
| |
| <p><a name="index-C-and-C_0040t_007b_002b_002b_007d-constants-987"></a> |
| <span class="sc">gdb</span> allows you to express the constants of C and C<tt>++</tt> in the |
| following ways: |
| |
| <ul> |
| <li>Integer constants are a sequence of digits. Octal constants are |
| specified by a leading ‘<samp><span class="samp">0</span></samp>’ (i.e. zero), and hexadecimal constants |
| by a leading ‘<samp><span class="samp">0x</span></samp>’ or ‘<samp><span class="samp">0X</span></samp>’. Constants may also end with a letter |
| ‘<samp><span class="samp">l</span></samp>’, specifying that the constant should be treated as a |
| <code>long</code> value. |
| |
| <li>Floating point constants are a sequence of digits, followed by a decimal |
| point, followed by a sequence of digits, and optionally followed by an |
| exponent. An exponent is of the form: |
| ‘<samp><span class="samp">e[[+]|-]</span><var>nnn</var><span class="samp"><!-- /@w --></span></samp>’, where <var>nnn</var> is another |
| sequence of digits. The ‘<samp><span class="samp">+</span></samp>’ is optional for positive exponents. |
| A floating-point constant may also end with a letter ‘<samp><span class="samp">f</span></samp>’ or |
| ‘<samp><span class="samp">F</span></samp>’, specifying that the constant should be treated as being of |
| the <code>float</code> (as opposed to the default <code>double</code>) type; or with |
| a letter ‘<samp><span class="samp">l</span></samp>’ or ‘<samp><span class="samp">L</span></samp>’, which specifies a <code>long double</code> |
| constant. |
| |
| <li>Enumerated constants consist of enumerated identifiers, or their |
| integral equivalents. |
| |
| <li>Character constants are a single character surrounded by single quotes |
| (<code>'</code>), or a number—the ordinal value of the corresponding character |
| (usually its <span class="sc">ascii</span> value). Within quotes, the single character may |
| be represented by a letter or by <dfn>escape sequences</dfn>, which are of |
| the form ‘<samp><span class="samp">\</span><var>nnn</var></samp>’, where <var>nnn</var> is the octal representation |
| of the character's ordinal value; or of the form ‘<samp><span class="samp">\</span><var>x</var></samp>’, where |
| ‘<samp><var>x</var></samp>’ is a predefined special character—for example, |
| ‘<samp><span class="samp">\n</span></samp>’ for newline. |
| |
| <p>Wide character constants can be written by prefixing a character |
| constant with ‘<samp><span class="samp">L</span></samp>’, as in C. For example, ‘<samp><span class="samp">L'x'</span></samp>’ is the wide |
| form of ‘<samp><span class="samp">x</span></samp>’. The target wide character set is used when |
| computing the value of this constant (see <a href="Character-Sets.html#Character-Sets">Character Sets</a>). |
| |
| <li>String constants are a sequence of character constants surrounded by |
| double quotes (<code>"</code>). Any valid character constant (as described |
| above) may appear. Double quotes within the string must be preceded by |
| a backslash, so for instance ‘<samp><span class="samp">"a\"b'c"</span></samp>’ is a string of five |
| characters. |
| |
| <p>Wide string constants can be written by prefixing a string constant |
| with ‘<samp><span class="samp">L</span></samp>’, as in C. The target wide character set is used when |
| computing the value of this constant (see <a href="Character-Sets.html#Character-Sets">Character Sets</a>). |
| |
| <li>Pointer constants are an integral value. You can also write pointers |
| to constants using the C operator ‘<samp><span class="samp">&</span></samp>’. |
| |
| <li>Array constants are comma-separated lists surrounded by braces ‘<samp><span class="samp">{</span></samp>’ |
| and ‘<samp><span class="samp">}</span></samp>’; for example, ‘<samp><span class="samp">{1,2,3}</span></samp>’ is a three-element array of |
| integers, ‘<samp><span class="samp">{{1,2}, {3,4}, {5,6}}</span></samp>’ is a three-by-two array, |
| and ‘<samp><span class="samp">{&"hi", &"there", &"fred"}</span></samp>’ is a three-element array of pointers. |
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