使用malloc()为const char字符串动态分配内存, [英] Dynamically allocating memory for const char string using malloc()
问题描述
我编写一个程序,从.ini文件读取一个值,然后将值传递给接受PCSTR(即const char *)的函数。函数 getaddrinfo()
。
因此,我想写 PCSTR ReadFromIni )
。要返回一个常量字符串,我计划使用 malloc()
分配内存并将内存转换为常量字符串。我将能够获得从.ini文件读取的字符的确切数量。
这种技术好吗?
以下示例在Visual Studio 2013中运行良好,并根据需要打印hello。
const char * m()
{
char * c =(char *)malloc * sizeof(char));
c =hello;
return(const char *)c;
}
int main(int argc,char * argv [])
{
const char * d = m();
std :: cout<< d; // use PCSTR
}
第二行是可怕的错误:
char * c =(char *)malloc sizeof(char));
//'c'设置为指向一块分配的内存(通常位于堆中)
c =hello;
//'c'设置为指向一个常量字符串(通常位于代码段或数据部分)
你分配变量 c
两次,所以很明显,第一个赋值没有意义。
它就像写:
int i = 5;
i = 6;
最重要的是,你会丢失分配的内存的地址,所以你不会
$ b p $ p>
char * m()
{
const char * s =hello;
char * c =(char *)malloc(strlen(s)+1);
strcpy(c,s);
return c;请记住,任何调用 char * p =
$ b < m()
也必须在以后调用 free(p)
... I am writing a program that reads a value from an .ini file, then passes the value into a function that accepts a PCSTR (i.e. const char *). The function is getaddrinfo()
.
So, I want to write PCSTR ReadFromIni()
. To return a constant string, I plan on allocating memory using malloc()
and casting the memory to a constant string. I will be able to get the exact number of characters that were read from the .ini file.
Is that technique okay? I don't really know what else to do.
The following example runs fine in Visual Studio 2013, and prints out "hello" as desired.
const char * m()
{
char * c = (char *)malloc(6 * sizeof(char));
c = "hello";
return (const char *)c;
}
int main(int argc, char * argv[])
{
const char * d = m();
std::cout << d; // use PCSTR
}
The second line is "horribly" wrong:
char* c = (char*)malloc(6*sizeof(char));
// 'c' is set to point to a piece of allocated memory (typically located in the heap)
c = "hello";
// 'c' is set to point to a constant string (typically located in the code-section or in the data-section)
You are assigning variable c
twice, so obviously, the first assignment has no meaning.
It's like writing:
int i = 5;
i = 6;
On top of that, you "lose" the address of the allocated memory, so you will not be able to release it later.
You can change this function as follows:
char* m()
{
const char* s = "hello";
char* c = (char*)malloc(strlen(s)+1);
strcpy(c,s);
return c;
}
Keep in mind that whoever calls char* p = m()
, will also have to call free(p)
at some later point...
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