带消息的断言()

发布于 2024-11-04 21:51:16 字数 220 浏览 1 评论 0原文

我看到某处断言以以下方式与消息一起使用：

assert(("message", condition));

这似乎工作得很好，除了 gcc 抛出以下警告：

warning: left-hand operand of comma expression has no effect

如何停止警告？

原文

I saw somewhere assert used with a message in the following way:

assert(("message", condition));

This seems to work great, except that gcc throws the following warning:

warning: left-hand operand of comma expression has no effect

How can I stop the warning?

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゛时过境迁 2024-11-11 21:51:16

使用-Wno-unused-value停止警告；（选项-Wall 包括-Wunused-value）。

我认为更好的是使用另一种方法，比如

assert(condition && "message");

Use -Wno-unused-value to stop the warning; (the option -Wall includes -Wunused-value).

I think even better is to use another method, like

assert(condition && "message");

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仅此而已 2024-11-11 21:51:16

Try：

#define assert__(x) for ( ; !(x) ; assert(x) )

这样使用：

assert__(x) {
    printf("assertion will fail\n"); 
}

仅当断言失败时才会执行该块。

重要提示：此方法将对表达式 x 求值两次，以防 x 求值为 错误！（第一次，当 for 循环检查其条件时；第二次，当 assert 评估传递的表达式时！）

Try:

#define assert__(x) for ( ; !(x) ; assert(x) )

use as such:

assert__(x) {
    printf("assertion will fail\n"); 
}

Will execute the block only when assert fails.

IMPORTANT NOTE: This method will evaluate expression x twice, in case x evaluates to false! (First time, when the for loop is checking its condition; second time, when the assert is evaluating the passed expression!)

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吃不饱 2024-11-11 21:51:16

如果要传递格式化消息，可以使用以下宏：

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <assert.h>

#define clean_errno() (errno == 0 ? "None" : strerror(errno))
#define log_error(M, ...) fprintf(stderr, "[ERROR] (%s:%d: errno: %s) " M "\n", __FILE__, __LINE__, clean_errno(), ##__VA_ARGS__)
#define assertf(A, M, ...) if(!(A)) {log_error(M, ##__VA_ARGS__); assert(A); }

然后像 printf 一样使用它：

// With no args
assertf(self != NULL,"[Server] Failed to create server.");

// With formatting args
assertf((self->socket = u_open(self->port)) != -1,"[Server] Failed to bind to port %i:",self->port);
// etc...

输出：

[错误]（../src/webserver.c:180: errno: 地址已在使用中）
[服务器] 无法绑定到端口 8080: webserver:
../src/webserver.c:180: server_run: 断言 `(self->socket =
u_open(self->port)) != -1' 失败。

基于http://c.learncodethehardway.org/book/ex20.html

If you want to pass a formatted message, you could use the following macros:

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <assert.h>

#define clean_errno() (errno == 0 ? "None" : strerror(errno))
#define log_error(M, ...) fprintf(stderr, "[ERROR] (%s:%d: errno: %s) " M "\n", __FILE__, __LINE__, clean_errno(), ##__VA_ARGS__)
#define assertf(A, M, ...) if(!(A)) {log_error(M, ##__VA_ARGS__); assert(A); }

Then use it like printf:

// With no args
assertf(self != NULL,"[Server] Failed to create server.");

// With formatting args
assertf((self->socket = u_open(self->port)) != -1,"[Server] Failed to bind to port %i:",self->port);
// etc...

Output:

[ERROR] (../src/webserver.c:180: errno: Address already in use)
[Server] Failed to bind to port 8080: webserver:
../src/webserver.c:180: server_run: Assertion `(self->socket =
u_open(self->port)) != -1' failed.

Based on http://c.learncodethehardway.org/book/ex20.html

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末が日狂欢 2024-11-11 21:51:16

按照传统，(void) 会向编译器传达您故意忽略表达式的信息：

/* picard.c, TNG S6E11. */
#define assertmsg(x, msg) assert(((void) msg, x))
assertmsg(2+2==5, "There! are! four! lights!");

By tradition, (void) communicates to the compiler that you are knowingly ignoring an expression:

/* picard.c, TNG S6E11. */
#define assertmsg(x, msg) assert(((void) msg, x))
assertmsg(2+2==5, "There! are! four! lights!");

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∞梦里开花 2024-11-11 21:51:16

我喜欢在 C 中这样做。这允许通过以下方式调用 assert：

assert(expression);
assert(expression, "reason");
assert(file, "cannot open %s", filename);

以下是代码：

#define assert(cond, ...) \
  if (!(cond)) \
    _assert(#cond, __FILE__, __LINE__, #__VA_ARGS__ __VA_OPT__(,) ##__VA_ARGS__)

void _assert (const char* snippet, const char* file, int line, const char* message, ...)
{
  print("assert failed %s:%d %s\n", file, line, snippet);
 
  if (*message)
  {
    va_list arg;
    va_start(arg, message);
    char* data = va_arg(arg, char*);
    vprintf(data, arg);
  }
}

I like to do it this way in C. This allows calling assert the following ways:

assert(expression);
assert(expression, "reason");
assert(file, "cannot open %s", filename);

Here is the code:

#define assert(cond, ...) \
  if (!(cond)) \
    _assert(#cond, __FILE__, __LINE__, #__VA_ARGS__ __VA_OPT__(,) ##__VA_ARGS__)

void _assert (const char* snippet, const char* file, int line, const char* message, ...)
{
  print("assert failed %s:%d %s\n", file, line, snippet);
 
  if (*message)
  {
    va_list arg;
    va_start(arg, message);
    char* data = va_arg(arg, char*);
    vprintf(data, arg);
  }
}

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星軌x 2024-11-11 21:51:16

对于意外的开关默认情况，选项是

assert(!"message");

For unexpected default case of a switch, an options is

assert(!"message");

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洒一地阳光 2024-11-11 21:51:16

接受 const char* 并返回 true 的函数可能会让您免受各种警告：

#include <assert.h>

int always_true(const char *msg) {
    return 1;
}

#define assert_msg(expr, msg) assert((expr) && always_true(msg))

A function that takes const char* and returns true would probably save you from all sorts of warnings:

#include <assert.h>

int always_true(const char *msg) {
    return 1;
}

#define assert_msg(expr, msg) assert((expr) && always_true(msg))

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枕头说它不想醒 2024-11-11 21:51:16

就我而言，我更改了 @pmg 的答案以便能够控制输出。 (... && "message") 对我不起作用。

#include <assert.h>
#include <stdio.h>

#define __DEBUG__ 1

assert ((1 == 1) && 
       (__DEBUG__ && printf("  - debug: check, ok.\n")) || !__DEBUG__);

In my case, I changed @pmg's answer to be able to control the output. The (... && "message") didn't work for me.

#include <assert.h>
#include <stdio.h>

#define __DEBUG__ 1

assert ((1 == 1) && 
       (__DEBUG__ && printf("  - debug: check, ok.\n")) || !__DEBUG__);

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枫以 2024-11-11 21:51:16

您可以编写自己的宏来提供与 _Static_assert(expr, msg) 相同的用法：

#include <assert.h>
#include <stdbool.h>
#include <stdio.h>


/*
 * void assert_msg(bool expr, const char *msg);
 */
#if !defined(NDEBUG)
#define assert_msg(expr, msg)   do                  \
{                                                   \
        const bool  e_ = expr;                      \
                                                    \
        if (!e_) {                                  \
                fputs(msg, stderr);                 \
                fputc('\n', stderr);                \
                assert(e_);                         \
        }                                           \
} while (0)
#else
#define assert_msg(expr, msg)   do                  \
{                                                   \
                                                    \
        if (!(expr))                                \
                warn_bug(msg);                      \
} while (0)
#endif

我还有一个宏 warn_bug() 来打印程序的名称，文件、行、函数、errno 值和字符串以及用户消息，即使断言已禁用。其背后的原因是它不会破坏程序，但会警告可能存在错误。不过，如果define(NDEBUG)，您可以将assert_msg定义为空。

You could write your own macro that provides the same usage of _Static_assert(expr, msg):

#include <assert.h>
#include <stdbool.h>
#include <stdio.h>


/*
 * void assert_msg(bool expr, const char *msg);
 */
#if !defined(NDEBUG)
#define assert_msg(expr, msg)   do                  \
{                                                   \
        const bool  e_ = expr;                      \
                                                    \
        if (!e_) {                                  \
                fputs(msg, stderr);                 \
                fputc('\n', stderr);                \
                assert(e_);                         \
        }                                           \
} while (0)
#else
#define assert_msg(expr, msg)   do                  \
{                                                   \
                                                    \
        if (!(expr))                                \
                warn_bug(msg);                      \
} while (0)
#endif

I also have a macro warn_bug() that prints the name of the program, the file, the line, the function, the errno value and string, and a user message, even if asserts are disabled. The reason behind it is that it won't break the program, but it will warn that a bug will probably be present. You could just define assert_msg to be empty if defined(NDEBUG), though.

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