string变量赋值给char *p指针

string strAction;char *pAction=NULL;pAction=(char*)malloc(strAction.length()+1);strncpy(pAction,strAction.c_str());if(pAction!=NULL){    free(pAction);    pAction=NULL;}

上面看似简单的程序，还是有不少的注意点

1. 如何将string变量赋值给char *指针变量

2.strncpy和strcpy区别

3. char数组和字符串的区别，字符串分配内存需要加一个字节\0

4.指针用完一定要释放，malloc和free配套使用

5.指针的初始化和释放过后置为NULL，防止野指针。

最后看下strcpy和strncpy的区别：

man男人给出的解释就非常的详细

NAME       strcpy, strncpy - copy a stringSYNOPSIS       #include <string.h>       char *strcpy(char *dest, const char *src);       char *strncpy(char *dest, const char *src, size_t n);DESCRIPTION       The  strcpy()  function  copies the string pointed to by src, including       the terminating null byte ('\0'), to the buffer  pointed  to  by  dest.       The  strings  may  not overlap, and the destination string dest must be       large enough to receive the copy.       The strncpy() function is similar, except that at most n bytes  of  src       are  copied.  Warning: If there is no null byte among the first n bytes       of src, the string placed in dest will not be null terminated.       If the length of src is less than n, strncpy() pads  the  remainder  of       dest with null bytes.       A simple implementation of strncpy() might be:       A simple implementation of strncpy() might be:           char*           strncpy(char *dest, const char *src, size_t n){               size_t i;               for (i = 0 ; i < n && src[i] != '\0' ; i++)                   dest[i] = src[i];               for ( ; i < n ; i++)                   dest[i] = '\0';               return dest;           }RETURN VALUE       The  strcpy()  and strncpy() functions return a pointer to the destina-       tion string dest.CONFORMING TO       SVr4, 4.3BSD, C89, C99.CONFORMING TO       SVr4, 4.3BSD, C89, C99.NOTES       Some programmers consider strncpy() to be inefficient and error  prone.       If  the  programmer knows (i.e., includes code to test!)  that the size       of dest is greater than the length of src, then strcpy() can be used.       If there is no terminating null byte in the first n characters of  src,       strncpy()  produces  an unterminated string in dest.  Programmers often       prevent this mistake by forcing termination as follows:           strncpy(buf, str, n);           if (n > 0)               buf[n - 1]= '\0';BUGS       If the destination string of a strcpy() is not large enough, then  any-       thing  might  happen.   Overflowing  fixed-length  string  buffers is a       favorite cracker technique for taking complete control of the  machine.       Any  time  a  program  reads  or copies data into a buffer, the program       first needs to check that there’s enough space.  This may  be  unneces-       sary  if you can show that overflow is impossible, but be careful: pro-       grams can get changed over time, in ways that may make  the  impossible       possible.