ES.34: Don't define a (C-style) variadic function
ES.34:不要定义C风格的可变参数函数
Reason（原因）
Not type safe. Requires messy cast-and-macro-laden code to get working right.
这种方式不是类型安全的。需要繁杂的类型转换和宏装载代码来保证正确动作。
Example（示例）
#include <cstdarg>
// "severity" followed by a zero-terminated list of char*s; write the C-style strings to cerr
void error(int severity ...)
{
va_list ap; // a magic type for holding arguments
va_start(ap, severity); // arg startup: "severity" is the first argument of error()
for (;;) {
// treat the next var as a char*; no checking: a cast in disguise
char* p = va_arg(ap, char*);
if (!p) break;
cerr << p << ' ';
}
va_end(ap); // arg cleanup (don't forget this)
cerr << '\n';
if (severity) exit(severity);
}
void use()
{
error(7, "this", "is", "an", "error", nullptr);
error(7); // crash
error(7, "this", "is", "an", "error"); // crash
const char* is = "is";
string an = "an";
error(7, "this", "is", an, "error"); // crash
}
Alternative: Overloading. Templates. Variadic templates.
可选项：重载，模板，可变参数模板。
#include <iostream>
void error(int severity)
{
std::cerr << '\n';
std::exit(severity);
}
template <typename T, typename... Ts>
constexpr void error(int severity, T head, Ts... tail)
{
std::cerr << head;
error(severity, tail...);
}
void use()
{
error(7); // No crash!
error(5, "this", "is", "not", "an", "error"); // No crash!
std::string an = "an";
error(7, "this", "is", "not", an, "error"); // No crash!
error(5, "oh", "no", nullptr); // Compile error! No need for nullptr.
}
Note（注意）
This is basically the way printf is implemented.
这是实现printf的基本方法。
Enforcement（实施建议）
-
Flag definitions of C-style variadic functions.
-
标记定义了C风格可变参数函数的情况。
-
Flag #include <cstdarg> and #include <stdarg.h>
-
标记代码中包含#include <cstdarg> 和 #include <stdarg.h>的情况。
原文链接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#-es34-dont-define-a-c-style-variadic-function
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