static in C

#include <stdio.h>
#include <stdlib.h>

char * favorite_fruit1(void);
char * favorite_fruit2(void);
void favorite_fruit3(char **);
int main(void) {
    char * fruit1 = favorite_fruit1();
    printf("%s\n", fruit1);

    char * fruit2 = favorite_fruit2();
    printf("%s\n", fruit2);

    char * fruit3 = NULL;
    favorite_fruit3(&fruit3);
    printf("%s\n", fruit3);

    printf("------END of CODE------");
    return EXIT_SUCCESS;
}
char * favorite_fruit1(void){
    char deciduous[] = "apple";
    return deciduous;
}
char * favorite_fruit2(void){
    static char deciduous[] = "apple";
    return deciduous;
}
void favorite_fruit3(char ** fruit){
    static char deciduous[] = "apple";
    *fruit = deciduous;
}

favorite_fruit1很明顯會(huì)出現(xiàn)問(wèn)題，原因是因?yàn)?span style="color: #7f0055">char deciduous[]是局部變量，在函數(shù)調(diào)用返回后，就釋放了。

favorite_fruit2因?yàn)槭褂昧藄tatic，而static限定了變量被保存在數(shù)據(jù)段（data segment）中，它的聲明周期同程序一樣長(zhǎng)。所以不會(huì)出錯(cuò)。

favorite_fruit3是另一種有效的寫法，其原理同2。

posted on 2009-05-24 18:17 volnet 閱讀(1092) 評(píng)論(3)  編輯 收藏 引用 所屬分類: C/C++ 、algorithm