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36 .Nd memory reallocation function
42 .Fn reallocarray "void *ptr" "size_t nmemb" "size_t size"
46 function is similar to the
53 and checks for integer overflow in the calculation
60 function returns a pointer to the allocated space; otherwise, a
62 pointer is returned and
69 when there is multiplication in the
75 For example, avoid this common idiom as it may lead to integer overflow:
76 .Bd -literal -offset indent
77 if ((p = malloc(num * size)) == NULL)
81 A drop-in replacement is the
85 .Bd -literal -offset indent
86 if ((p = reallocarray(NULL, num, size)) == NULL)
87 err(1, "reallocarray");
92 be careful to avoid the following idiom:
93 .Bd -literal -offset indent
95 if ((p = realloc(p, size)) == NULL)
99 Do not adjust the variable describing how much memory has been allocated
100 until the allocation has been successful.
101 This can cause aberrant program behavior if the incorrect size value is used.
102 In most cases, the above sample will also result in a leak of memory.
103 As stated earlier, a return value of
105 indicates that the old object still remains allocated.
106 Better code looks like this:
107 .Bd -literal -offset indent
109 if ((newp = realloc(p, newsize)) == NULL) {
121 it is important to ensure the new size value will not overflow;
122 i.e. avoid allocations like the following:
123 .Bd -literal -offset indent
124 if ((newp = realloc(p, num * size)) == NULL) {
130 .Bd -literal -offset indent
131 if ((newp = reallocarray(p, num, size)) == NULL) {
139 function first appeared in