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<a name="Implementation-limits"></a>
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Next: <a rel="next" accesskey="n" href="Obsolete-Features.html#Obsolete-Features">Obsolete Features</a>,
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Previous: <a rel="previous" accesskey="p" href="Implementation_002ddefined-behavior.html#Implementation_002ddefined-behavior">Implementation-defined behavior</a>,
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Up: <a rel="up" accesskey="u" href="Implementation-Details.html#Implementation-Details">Implementation Details</a>
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<h3 class="section">11.2 Implementation limits</h3>
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<p><a name="index-implementation-limits-112"></a>
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CPP has a small number of internal limits. This section lists the
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limits which the C standard requires to be no lower than some minimum,
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and all the others known. It is intended that there should be as few limits
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as possible. If you encounter an undocumented or inconvenient limit,
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please report that as a bug. See <a href="../gcc/Bugs.html#Bugs">Reporting Bugs</a>.
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<p>Where we say something is limited <dfn>only by available memory</dfn>, that
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means that internal data structures impose no intrinsic limit, and space
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is allocated with <code>malloc</code> or equivalent. The actual limit will
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therefore depend on many things, such as the size of other things
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allocated by the compiler at the same time, the amount of memory
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consumed by other processes on the same computer, etc.
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<ul>
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<li>Nesting levels of ‘<samp><span class="samp">#include</span></samp>’ files.
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<p>We impose an arbitrary limit of 200 levels, to avoid runaway recursion.
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The standard requires at least 15 levels.
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<li>Nesting levels of conditional inclusion.
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<p>The C standard mandates this be at least 63. CPP is limited only by
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available memory.
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<li>Levels of parenthesized expressions within a full expression.
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<p>The C standard requires this to be at least 63. In preprocessor
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conditional expressions, it is limited only by available memory.
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<li>Significant initial characters in an identifier or macro name.
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<p>The preprocessor treats all characters as significant. The C standard
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requires only that the first 63 be significant.
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<li>Number of macros simultaneously defined in a single translation unit.
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<p>The standard requires at least 4095 be possible. CPP is limited only
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by available memory.
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<li>Number of parameters in a macro definition and arguments in a macro call.
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<p>We allow <code>USHRT_MAX</code>, which is no smaller than 65,535. The minimum
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required by the standard is 127.
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<li>Number of characters on a logical source line.
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<p>The C standard requires a minimum of 4096 be permitted. CPP places
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no limits on this, but you may get incorrect column numbers reported in
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diagnostics for lines longer than 65,535 characters.
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<li>Maximum size of a source file.
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<p>The standard does not specify any lower limit on the maximum size of a
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source file. GNU cpp maps files into memory, so it is limited by the
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available address space. This is generally at least two gigabytes.
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Depending on the operating system, the size of physical memory may or
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may not be a limitation.
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