在C中清空char字符串的最佳方法是什么？

Question

Hi I have a char string

name[50] = "I love programming"

what happen is that I want to empty this string before I call my another function so that I can store something in the same array

will this work?

name[0] = '\\0';

or is there anyway to empty the string without creating any new function or use any other library?

Answer 1

Setting first char to nul is perfectly acceptable. But if that string was sensitive in terms of security, then you should zero it out with memset .

Edit:

Answer from Matteo Italia made me dig a bit deeper on this subject. According to this document (and Matteos answer) memset could be optimized away, and so is not the best option to remove sensitive information from memory. The document has several options, but none of them is portable and reliable, so it proposes new function standard memset_s just for such purposes. This function does not exist yet, so we're currently stuck with non-portable ( SecureZeroMemory ), non-reliable ( volatile trick), or non-optimal options ( secure_memset example).

Answer 2

There's really no concept of emptying a char string in C. It's simply a pointer that points to some allocated memory. You can reuse that memory in any way you wish, without "emptying" it first. So, the easiest way to empty it is "just don't".

If you want to explicitly clear all contents of the string for some reason, use the memset approach given in other answers.

If you want to "empty" it in the sense that when it's printed, nothing will be printed, then yes, just set the first char to `\\0'.

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To conclude, it all depends on what you really want to do. Why do you want to "empty" the string?

Answer 3

Use memset instead. This would just nullify the buffer but the memory allocated would any how gets deallocated from stack when the variable goes out of scope.

memset (name,'\0',sizeof(name));

Answer 4

IIRC, you might use memset this way:

char * myString;
...
size_t len = strlen(myString)
memset (myString, 0,len);

Answer 5

Tehnically it is correct, for example:

char array[10] = "hello";
printf("%d\r\n", strlen(array)); // prints 5
array[0] = '\0';
printf("%d\r\n", strlen(array)); // prints 0

Answer 6

memset(name, 0, 50); 

要么

bzero(name, 50);

Answer 7

It depends from the effect you want to obtain. If you just want to zero its length you can do, as you said:

*name='\0';

If, instead, you want to clean your string from sensitive data, you should zero it completely with memset (some operating systems also have a "secure" zeroing function that should be guaranteed not to be optimized away by the compiler - see eg SecureZeroMemory on Windows).

On the other hand, if the function you are calling just uses the buffer you are passing as an output buffer disregarding its content, you may just leave the buffer as it is.