1assert(3) Library Functions Manual assert(3)
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6 assert - abort the program if assertion is false
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9 Standard C library (libc, -lc)
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12 #include <assert.h>
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14 void assert(scalar expression);
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17 This macro can help programmers find bugs in their programs, or handle
18 exceptional cases via a crash that will produce limited debugging out‐
19 put.
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21 If expression is false (i.e., compares equal to zero), assert() prints
22 an error message to standard error and terminates the program by call‐
23 ing abort(3). The error message includes the name of the file and
24 function containing the assert() call, the source code line number of
25 the call, and the text of the argument; something like:
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27 prog: some_file.c:16: some_func: Assertion `val == 0' failed.
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29 If the macro NDEBUG is defined at the moment <assert.h> was last in‐
30 cluded, the macro assert() generates no code, and hence does nothing at
31 all. It is not recommended to define NDEBUG if using assert() to de‐
32 tect error conditions since the software may behave non-deterministi‐
33 cally.
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36 No value is returned.
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39 For an explanation of the terms used in this section, see at‐
40 tributes(7).
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42 ┌────────────────────────────────────────────┬───────────────┬─────────┐
43 │Interface │ Attribute │ Value │
44 ├────────────────────────────────────────────┼───────────────┼─────────┤
45 │assert() │ Thread safety │ MT-Safe │
46 └────────────────────────────────────────────┴───────────────┴─────────┘
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49 C11, POSIX.1-2008.
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52 C89, C99, POSIX.1-2001.
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54 In C89, expression is required to be of type int and undefined behavior
55 results if it is not, but in C99 it may have any scalar type.
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58 assert() is implemented as a macro; if the expression tested has side-
59 effects, program behavior will be different depending on whether NDEBUG
60 is defined. This may create Heisenbugs which go away when debugging is
61 turned on.
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64 abort(3), assert_perror(3), exit(3)
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68Linux man-pages 6.04 2023-03-30 assert(3)