Secure template overloads
Microsoft has deprecated many C Runtime library (CRT) functions in favor of security-enhanced versions. For example, strcpy_s
is the more secure replacement for strcpy
. The deprecated functions are common sources of security bugs, because they don't prevent operations that can overwrite memory. By default, the compiler produces a deprecation warning when you use one of these functions. The CRT provides C++ template overloads for these functions to help ease the transition to the more secure variants.
For example, this code snippet generates a warning because strcpy
is deprecated:
char szBuf[10];
strcpy(szBuf, "test"); // warning: deprecated
The deprecation warning is there to tell you that your code may be unsafe. If you've verified that your code can't overwrite memory, you have several choices. You can choose to ignore the warning, you can define the symbol _CRT_SECURE_NO_WARNINGS
before the include statements for the CRT headers to suppress the warning, or you can update your code to use strcpy_s
:
char szBuf[10];
strcpy_s(szBuf, 10, "test"); // security-enhanced _s function
The template overloads provide more choices. If you define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES
to 1, it enables template overloads of standard CRT functions that call the more secure variants automatically. If _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES
is 1, then no changes to your code are necessary. Behind the scenes, the call to strcpy
is changed to a call to strcpy_s
with the size argument supplied automatically.
#define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES 1
// ...
char szBuf[10];
strcpy(szBuf, "test"); // ==> strcpy_s(szBuf, 10, "test")
The macro _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES
doesn't affect the functions that take a count, such as strncpy
. To enable template overloads for the count functions, define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES_COUNT
to 1. Before doing so, however, make sure that your code passes the count of characters, not the size of the buffer (a common mistake). Also, code that explicitly writes a null terminator at the end of the buffer after the function call is unnecessary if the secure variant is called. If you need truncation behavior, see _TRUNCATE
.
Note
The macro _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES_COUNT
requires that _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES
is also defined as 1. If _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES_COUNT
is defined as 1 and _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES
is defined as 0, the application will not perform any template overloads.
When you define _CRT_SECURE_CPP_OVERLOAD_SECURE_NAMES
to 1, it enables template overloads of the secure variants (names ending in "_s"). In this case, if _CRT_SECURE_CPP_OVERLOAD_SECURE_NAMES
is 1, then one small change must be made to the original code:
#define _CRT_SECURE_CPP_OVERLOAD_SECURE_NAMES 1
// ...
char szBuf[10];
strcpy_s(szBuf, "test"); // ==> strcpy_s(szBuf, 10, "test")
Only the name of the function needs to be changed (by adding "_s"); the template overload takes care of providing the size argument.
By default, _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES
and _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES_COUNT
are defined as 0 (disabled) and _CRT_SECURE_CPP_OVERLOAD_SECURE_NAMES
is defined as 1 (enabled).
The template overloads only work for static arrays. Dynamically allocated buffers require other source code changes. Revisiting the above examples:
#define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES 1
// ...
char *szBuf = (char*)malloc(10);
strcpy(szBuf, "test"); // still deprecated; change it to
// strcpy_s(szBuf, 10, "test");
And this example:
#define _CRT_SECURE_CPP_OVERLOAD_SECURE_NAMES 1
// ...
char *szBuf = (char*)malloc(10);
strcpy_s(szBuf, "test"); // doesn't compile; change it to
// strcpy_s(szBuf, 10, "test");
See also
Security features in the CRT
C runtime (CRT) and C++ Standard Library (STL) .lib
files
Povratne informacije
https://aka.ms/ContentUserFeedback.
Kmalu na voljo: V letu 2024 bomo ukinili storitev Težave v storitvi GitHub kot mehanizem za povratne informacije za vsebino in jo zamenjali z novim sistemom za povratne informacije. Za več informacij si oglejte:Pošlji in prikaži povratne informacije za