c语言实现简单的string

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前言

在c语言中利用面向对象的编程方式，实现类似c++中的string类。

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一、注意事项

所有与string结构体相关的函数全都没有返回值。
在c++中，当产生临时对象时编译器会自动的加入析构函数，销毁临时变量；但是C语言中必须手动显示的写出析构函数，当string结构体相关函数返回临时变量时，必须降临时变量显示赋值，或者当场调用析构函数，否则非常容易造成内存泄露。索性就都没有返回值。

二、代码

#include 
#include 
#include 

/**
 * 若对string相关函数提供返回值则非常容易造成内存泄露，因此所有函数都不提供返回值
*/

typedef struct _string
{
    char* ptr;
    int num;
} string;
void string_Ctor(string* s)
{
    memset(s, 0, sizeof(string));
}
void string_Dtor(string* s)
{
    free(s->ptr);
    memset(s, 0, sizeof(string));
}
void string_add(string* all, string s1, string s2)
{
    string sum; string_Ctor(&sum);
    sum.num = s1.num + s2.num;
    sum.ptr = (char*)malloc(sum.num + 1);
    memcpy(sum.ptr, s1.ptr, s1.num);
    memcpy(sum.ptr+s1.num, s2.ptr, s2.num);
    sum.ptr[sum.num] = '\0';
    string_Dtor(all);
    *all = sum;
}
void string_assign_s_p(string* str, char* ptr)
{
    if (str->ptr == ptr) return;
    string_Dtor(str);
    str->num = strlen(ptr);
    str->ptr = (char*)malloc(str->num+1);
    memcpy(str->ptr, ptr, strlen(ptr));
    str->ptr[str->num] = '\0';
}
void string_assign_s_s(string* str1, string* str2)
{
    if (str1 == str2) return;
    string_Dtor(str1);
    str1->num = str2->num;
    str1->ptr = (char*)malloc(str1->num + 1);
    memcpy(str1->ptr, str2->ptr, str1->num);
    str1->ptr[str1->num] = '\0';
}
void string_add_assign(string* str1, string* str2)
{
    string sum; string_Ctor(&sum);
    string_add(&sum, *str1, *str2);
    string_Dtor(str1);
    *str1 = sum;
}


int main() {
    string http_head, http_body, http_msg;
    string_Ctor(&http_head); string_Ctor(&http_body); string_Ctor(&http_msg);

    string_assign_s_p(&http_head, "abc""def");
    string_assign_s_p(&http_msg, "jskldfj;laskjdflkj");
    string_add_assign(&http_msg, &http_head);
    string_assign_s_s(&http_body, &http_msg);
    string_add(&http_head, http_body, http_msg);

    printf("%s\n", http_head.ptr);

    string_Dtor(&http_head); string_Dtor(&http_body); string_Dtor(&http_msg);
}

valgrind扫描

Valgrind——c/c++内存检测工具

==23054== Memcheck, a memory error detector
==23054== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==23054== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==23054== Command: ./a.out
==23054== Parent PID: 18533
==23054== 
==23054== 
==23054== HEAP SUMMARY:
==23054==     in use at exit: 0 bytes in 0 blocks
==23054==   total heap usage: 6 allocs, 6 frees, 1,149 bytes allocated
==23054== 
==23054== All heap blocks were freed -- no leaks are possible
==23054== 
==23054== For lists of detected and suppressed errors, rerun with: -s
==23054== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

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总结

虽然可以利用面向对象的思想实现类似的c++中的string类，但是由于受到c语言语法的限制，不能像写c++一样写C，如析构函数必须显示写出。