lemene

說明

使用char[]和char*定義變量，并賦值字符串常量，這兩者有較大區別。前者定義數組，并將字符串常量拷貝至該數組，變量表示這個新數組的首地址。后者定義指針，指向一個字符常量。前者會產生新的字符串數據，并且擁有讀寫權限，后者不一定產生新字符串數據，并且只有讀權限。

實驗代碼

/**
 * @file char_array_pointer.cpp
 * @brief 測試字符數組和指針
 * @copyrigh public domain
 */
#include <iostream>
const char* string0() {
const char* str = "string";
return str;
}
const char* string1() {
return "string";
}
const char* string2() {
static const char str[] = "string";
return str;
}
const char* string3() {
    char str[] = "string";
    return str;
}
void function() {
    char a[] = "abc123456";
}
void test_string1() {
    const char* str = string1();
    std::cout << "test_string1: " << str << std::endl;
    function();
    std::cout << "test_string1: " << str << std::endl;
}
void test_string2() {
    const char* str = string2();
    std::cout << "test_string2: " << str << std::endl;
    function();
    std::cout << "test_string2: " << str << std::endl;
}
void test_string3() {
    const char* str = string3();
    std::cout << "test_string3: " << str << std::endl;
    function();
    std::cout << "test_string3: " << str << std::endl;
}
int main() {
std::cout << "string0 == string1 is " << (string0() == string1() ? "true" : "false") << std::endl;
std::cout << "string1 == string2 is " << (string1() == string2() ? "true" : "false") << std::endl;
    test_string1();
    test_string2();
    test_string3();
    return 0;
}

運行及結果

$ g++ char_array_pointer.cpp
char_array_pointer.cpp: In function 'const char* string3()':
char_array_pointer.cpp:24:10: warning: address of local variable 'str' returned [enabled by default]

$ ./a.exe
string0 == string1 is true
string1 == string2 is false
test_string1: string
test_string1: string
test_string2: string
test_string2: string
test_string3: string
test_string3: abc12345YP@