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54 lines
2.3 KiB
C
54 lines
2.3 KiB
C
/* vla.h - variable length arrays
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Copyright 2014-2020 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>.
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Written by Paul Eggert. */
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/* The VLA_ELEMS macro does not allocate variable-length arrays (VLAs),
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so it does not have the security or performance issues commonly
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associated with VLAs. VLA_ELEMS is for exploiting a C11 feature
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where a function can start like this:
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double scan_array (int n, double v[static n])
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to require a caller to pass a vector V with at least N elements;
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this allows better static checking and performance in some cases.
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In C11 this feature means that V is a VLA, so the feature is
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supported only if __STDC_NO_VLA__ is defined, and for compatibility
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to platforms that do not support VLAs, VLA_ELEMS (n) expands to
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nothing when __STDC_NO_VLA__ is not defined. */
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/* A function's argument must point to an array with at least N elements.
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Example: 'int main (int argc, char *argv[VLA_ELEMS (argc)]);'. */
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#ifdef __STDC_NO_VLA__
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# define VLA_ELEMS(n)
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#else
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# define VLA_ELEMS(n) static n
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#endif
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/* Although C99 requires support for variable-length arrays (VLAs),
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some C compilers never supported VLAs and VLAs are optional in C11.
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VLAs are controversial because their allocation may be unintended
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or awkward to support, and large VLAs might cause security or
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performance problems. GCC can diagnose the use of VLAs via the
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-Wvla and -Wvla-larger-than warnings options, and defining the
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macro GNULIB_NO_VLA disables the allocation of VLAs in Gnulib code.
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The VLA_ELEMS macro is unaffected by GNULIB_NO_VLA, since it does
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not allocate VLAs. Programs that use VLA_ELEMS should be compiled
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with 'gcc -Wvla-larger-than' instead of with 'gcc -Wvla'. */
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