問題1：
字符數(shù)組名可以作為左值嗎？當然不行
比如?
char str[20] = {'h','e','l','l','o',' ','w','o','r','l','d'};
str++;
不可以這么干，因為字符數(shù)組名是一個常量指針，也就是是一個const char*
#include <stdio.h>
int main()
{
char str[20] = {'h','e','l','l','o',' ','w','o','r','l','d'};
printf("sizeof(str): %d\n",sizeof(str));
printf("str: %s\n",str);
str = str + 1; //error
return 0;
}運行結(jié)果如下：
當數(shù)組名為左值時，它的類型是字符數(shù)組；當數(shù)組名為右值時，它的數(shù)據(jù)類型是字符指針。
#include <stdio.h>
#include <string.h>
int main(void)
{
char buf[10];
char *p= “afdal”;
buf = p; //將一個char* 賦給一個char[10]，類型不一樣，必然不成功
printf(“the buf is:%s\n”,buf);
return 0;
}問題2：
字符數(shù)組如何進行初始化？
#include <stdio.h>
int main()
{
char ptr[20] = "hello world"; //success
char str[20] = {'h','e','l','l','o',' ','w','o','r','l','d'}; //success
char ctr[20];
ctr = "hello world"; // error: incompatible types when assigning to type ‘char[20]’ from type ‘char *’
return 0;
}在給字符數(shù)組初始化的時候，會自動在字符數(shù)組的結(jié)尾加上'\0'
#include <stdio.h>
int main()
{
char str[20] = {'h','e','l','l','o',' ','w','o','r','l','d'};
printf("sizeof(str): %d\n",sizeof(str));
printf("str: %s\n",str);
int i = 0;
while(*(str + i) != '\0') //判斷是否加上'\0'
{
printf("%c\n",*( str + i++));
}
return 0;
}運行結(jié)果如下：
問題3：
字符數(shù)組越界訪問能編譯通過嗎？
字符數(shù)組越界訪問編譯可以通過，沒有報錯，這樣會出現(xiàn)很多的問題
#include <stdio.h>
int main()
{
char str[12] = {'h','e','l','l','o',' ','w','o','r','l','d'};
printf("%c\n",str[100]);
return 0;
}
打印為空
問題4：
字符數(shù)組和字符指針又有什么區(qū)別呢？
首先在內(nèi)存的中位置不同，字符數(shù)組保存的字符串存放在內(nèi)存的棧中，而字符指針指向的字符串保存在內(nèi)存的靜態(tài)存儲區(qū)中。
其次字符數(shù)組保存的字符串屬于字符串變量，可以被修改，而字符指針指向的字符串是屬于字符串常量，不能被修改。
#include <stdio.h>
int main()
{
char str[12] = {'h','e','l','l','o',' ','w','o','r','l','d'};
char* ptr = "hello world";
str[0] = 'f';
ptr[0] = 'f'; //將字符指針指向的字符串修改，將出現(xiàn)段錯誤，因為該內(nèi)存地址只讀，因為該字符串屬于常量
return 0;
}運行結(jié)果：
段錯誤是指訪問的內(nèi)存超出了系統(tǒng)給這個程序所設(shè)定的內(nèi)存空間，例如訪問了不存在的內(nèi)存地址、訪問了系統(tǒng)保護的內(nèi)存地址、訪問了只讀的內(nèi)存地址等等情況。
#include <stdio.h>
int main()
{
char* ptr = "hello world";
ptr[11] = '!'; //往常量字符串末尾添加字符，相當于連接兩個字符串，出錯
ptr[12] = '\0';
return 0;
}這樣也會出現(xiàn)段錯誤。
問題5：
字符指針是不是和字符數(shù)組名都是指針常量呢？
不是，字符指針，可以改變它的指向，也就是可以為左值?？梢詫⒁粋€字符指針指向一個字符串常量后又指向另外一個字符串常量。字符指針在為初始化之前，他是一個未定義的值，將指向任何可能的地方，所以在使用字符指針時一定要注意初始化。
#include <stdio.h>
int main()
{
char* ptr;
printf("ptr: %c\n",*ptr);
return 0;
}運行結(jié)果：
編譯可以通過，但是ptr指向的內(nèi)存地址是任意的
當然也可以將一個字符指針指向一個字符數(shù)組。
#include <stdio.h>
int main()
{
char str[12] = {'h','e','l','l','o',' ','w','o','r','l','d'};
char* ptr = str;
printf("ptr: %s\n",ptr);
return 0;
}運行結(jié)果：
問題6：
如果一個字符指針指向一個堆中動態(tài)內(nèi)存。那么我們?nèi)绾纬跏蓟搩?nèi)存中的值？
#include <stdio.h>
#include <stdlib.h>
int main()
{
char* str = (char*)malloc(sizeof(char)*20);
printf("str:%p\n",str); //str在堆中內(nèi)存首地址
str = "hello world";
printf("str:%p\n",str); //str在靜態(tài)存儲區(qū)內(nèi)存首地址
char* ptr = "I love you";
printf("ptr:%p\n",ptr); //str在靜態(tài)存儲區(qū)內(nèi)存首地址
return 0;
}運行結(jié)果如下：
很明顯前后的地址不一樣，前一個指向堆中的內(nèi)存的地址，而后一個指向了靜態(tài)存儲區(qū)中的內(nèi)存的地址。我本以為我通過上述方式進行初始化str的時候，我可以將堆中內(nèi)存進行初始化，我發(fā)現(xiàn)我錯了，字符指針將被重新指向。但是我想如果我們將str聲明為const呢？那將會出現(xiàn)什么樣的結(jié)果呢？
#include <stdio.h>
#include <stdlib.h>
int main()
{
const char* str = (char*)malloc(sizeof(char)*20); //我以為const將修飾str，使得str不能再作為左值而出現(xiàn)，我錯了，const修飾的是由str指向的字符串，
printf("str:%p\n",str); //該字符串不能再被修改
str = "hello world";
printf("str:%p\n",str);
return 0;
}運行結(jié)果：
如果我們將上述的代碼做如下修改，程序還能編譯通過嗎？
#include <stdio.h>
#include <stdlib.h>
int main()
{
const char* str = (char*)malloc(sizeof(char)*20);
printf("str:%p\n",str);
str[0] = 'h'; //這種賦值才是對str原來所指向的堆中的內(nèi)存的賦值，編譯不過，因為str指向的堆中的內(nèi)存是只讀的。
str = "hello world";
printf("str:%p\n",str);
return 0;
}運行結(jié)果如下：
上述就引發(fā)了我思考為什么const修飾的是str指向的字符串，而不是str本身呢？
原來，char* const str才是真正的修飾str本身，使得str為只讀的，不能再被修改，也就是重新指向其他內(nèi)存地址。而const char* str 和 char const* str 的意義是一致的，都是修飾的是*str。
#include <stdio.h>
#include <stdlib.h>
int main()
{
char* const str = (char*)malloc(sizeof(char)*20);
printf("str:%p\n",str);
str[0] = 'h';
str = "hello world"; //變量str被重新指向，error，編譯不過
printf("str:%p\n",str);
return 0;
}運行結(jié)果如下：
那么我們又該如何初始化一個字符指針指向的內(nèi)存呢？
其實我們可以很清楚的分析，如果str是一個字符指針，也就是一個變量，變量是可以被重新賦值的，而每一個字符串本身是有一個地址的，str = “hello world”，必然就是改變了str的值，使得str保存著"hello world"的內(nèi)存首地址，而一旦你將str = "I love you"，必然str將保存這"I love you"的內(nèi)存首地址，這都是毋庸置疑的。
#include <stdio.h>
int main()
{
printf("hello world:%p\n","hello world"); //將打印出"hello world"的內(nèi)存地址
printf("I love you:%p\n","I love you"); //將打印出"I love you"的內(nèi)存地址
return 0;
}運行如下：
下面我得回到這樣一個問題？
str 和 *str的區(qū)別，很明顯，str是一個指針，而*str是str指向的內(nèi)存的存放的值，既然我們想改變str指向內(nèi)存中的值，既*str的值，那么為何不將*str作為左值，來初始化str所指向內(nèi)存的值呢？而*str 不就是 str[0]嗎？所以很明顯了。上述問題：那么我們又該如何初始化一個字符指針指向的內(nèi)存呢？當然這個僅限于字符指針指向的是由mlloc分配的堆中的內(nèi)存以及字符數(shù)組指向的棧中的內(nèi)存。而字符指針如果指向字符常量，不可修改字符指針指向的內(nèi)存的值，因為字符常量是只讀的。
#include <stdio.h>
#include <stdlib.h>
int main()
{
char* const str = (char*)malloc(sizeof(char)*20);
printf("str:%p\n",str);
str[0] = 'A'; //數(shù)組下標型賦值
*(str + 1) = 'l'; //指針++型賦值
str[2] = 'e',
*(str + 3) = 'x';
printf("str:%s\n",str);
printf("str:%p\n",str);
return 0;
}運行如下：
#include <stdio.h>
#include <stdlib.h>
int main()
{
char str[20];
printf("str:%p\n",str);
str[0] = 'A';
*(str + 1) = 'l';
str[2] = 'e',
*(str + 3) = 'x';
//str[4] = '\0'; //當我們沒有手動給字符串結(jié)尾附上'\0'
printf("str:%s\n",str);
printf("str:%p\n",str);
return 0;
}運行如下：
上述的運行結(jié)果說明上述程序并沒有自動給字符串結(jié)尾附上'\0'，對于字符數(shù)組除非這樣賦值，str[20] = "hello world"，不然你就得手動給字符串附上字符串結(jié)尾'\0'。
#include <stdio.h>
#include <stdlib.h>
int main()
{
char str[20];
printf("str:%p\n",str);
str[0] = 'A';
*(str + 1) = 'l';
str[2] = 'e',
*(str + 3) = 'x';
str[4] = '\0';
printf("str:%s\n",str);
printf("str:%p\n",str);
return 0;
}
~運行結(jié)果：
附上一段我關(guān)于memcpy()和memmove()的代碼的實現(xiàn)。
#include <stdio.h>
#include <stdlib.h>
void mem_copy(char* const dest, const char* const src)
{
for(int i = 0; *(src + i) != '\0'; i++)
*(dest + i) = *(src + i);
}
void mem_move(char* const dest, const char* const src)
{
int i = 0;
while(*(src + i) != '\0')
i++;
for(; i != -1; i--)
*(dest + i) = *(src + i);
}
int main()
{
char* src = "hello world";
char* const dest1 = (char*)malloc(sizeof(char) * 20);
char dest2[20];
mem_copy(dest1,src);
mem_move(dest2,src);
printf("dest1:%s\n",dest1);
printf("dest2:%s\n",dest2);
return 0;
}當我們需要將內(nèi)存的中的某一地址段的內(nèi)容拷貝到內(nèi)存中另一地址段中，以上是將字符串常量區(qū)的內(nèi)容拷貝到堆中和棧中，我們可以看到我分別使用了malloc和字符數(shù)組，當然我們得考慮可能在拷貝的過程中會有地址段重疊的問題，重疊該怎么拷貝，解決方案很簡單，就是從尾向前拷貝，即可。
運行結(jié)果如下：
以上是我對c語言中字符串操作的一些理解
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