(原創) 如何对array或struct做初始化? (memset()) (C/C++) (C)
当宣告C/C++的built-in type后,必须马上initialize该变量的值,因为C/C++在宣告变量时,仅为该变量配置了一块内存,却没对该变量设定任何初始值,所以该变量目前的值为宣告该变量前所残留的值,虽可直接使用该变量,但并没有任何意义。
尤其在使用array时,当宣告完array及其大小后,第一件事情就是为array中所有element设定初始值,通常我们会用for来设定
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#include <string.h>
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#include <stdio.h>
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#define ia_size 5
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int main() {
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int ia[ia_size];
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for(int i = 0; i != ia_size; ++i) {
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*ia = 0;
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}
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for(int i = 0; i != ia_size; ++i) {
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printf("%d",*ia);
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}
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return 0;
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}
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用for写最少要两行程序,若使用memset(),只要一行就可搞定
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/*
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(C) OOMusou 2006 http://oomusou.cnblogs.com
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Filename : memset0.cpp
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Compiler : Visual C++ 8.0 / gcc 4.1.0
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Description : The memset() function fills the first n
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bytes of the memory area pointed to by
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s with constant byte c.
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Synopsis : #include <string.h>
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void* memset(void* s, int c, size_t n);
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Release : 11/25/2006
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*/
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#include <string.h>
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#include <stdio.h>
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#define ia_size 5
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int main() {
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int ia[ia_size];
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memset(ia,0,sizeof(ia));
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for(int i = 0; i != ia_size; ++i) {
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printf("%d",*ia);
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}
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return 0;
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}
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memset()除了可以初始化array外,也可用来初始化struct
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/*
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(C) OOMusou 2006 http://oomusou.cnblogs.com
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Filename : memset1.cpp
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Compiler : Visual C++ 8.0 / gcc 4.1.0
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Description : The memset() function fills the first n
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bytes of the memory area pointed to by
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s with constant byte c.
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Synopsis : #include <string.h>
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void* memset(void* s, int c, size_t n);
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Release : 11/25/2006
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*/
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#include <string.h>
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#include <stdio.h>
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struct Foo {
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int no;
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double d;
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};
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int main() {
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Foo foo;
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memset(&foo,0,sizeof(foo));
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printf("%i\n",foo.no);
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printf("%d\n",foo.d);
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return 0;
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}
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Reference
Linux C函式库详解辞典 P.73, 徐千祥, 旗标出版社
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