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28 .\" @(#)assert.3 8.1 (Berkeley) 6/9/93
37 .Nd expression verification macro
41 .Fn static_assert expression
42 .Fn static_assert expression message
49 the calling process is terminated.
50 A diagnostic message is written to
54 is called, effectively terminating the program.
66 may be removed at compile time by defining
72 .Fl D Ns Dv NDEBUG ) .
73 Unlike most other include files,
75 may be included multiple times.
76 Each time whether or not
78 is defined determines the behavior of assert from that point forward
79 until the end of the unit or another include of
84 macro should only be used for ensuring the developer's expectations
86 It is not appropriate for regular run-time error detection.
94 makes assertions at compile-time.
95 Once the constraint is violated, the compiler produces a diagnostic
96 message including the string literal message, if provided.
97 The initial form of the
99 containing a string literal message was introduced in C11 standard, and
100 the other form with no string literal is to be implemented by C2x and
101 some compilers may lack its adoption at present.
104 .Dl "assert(1 == 0);"
105 generates a diagnostic message similar to the following:
106 .Dl "Assertion failed: (1 == 0), function main, file main.c, line 100."
108 The following assert tries to assert there was no partial read:
109 .Dl "assert(read(fd, buf, nbytes) == nbytes);"
110 However, there are two problems.
111 First, it checks for normal conditions, rather than conditions that
113 Second, the code will disappear if
115 is defined, changing the semantics of the program.
117 The following asserts that the size of the S structure is 16.
118 Otherwise, it produces a diagnostic message which points at the
119 constraint and includes the provided string literal:
120 .Dl "static_assert(sizeof(struct S) == 16, ""size mismatch"");"
121 If none is provided, it only points at the constraint.