C printf跨平台格式没有警告 [英] C printf cross-platform format without warnings

问题描述

你如何编写代码来编译跨平台而不需要警告。例如，我不会在x64平台上收到警告，但我会在ARM（树莓派）上做：

warning：format'％lu'expect the argument of type' long unsigned int'，但是参数5的类型是'size_t {aka unsigned int}

不用说我不想禁用警告。
$ b

更多示例和场景：

 警告：format'％lu'需要参数类型' long unsigned int'，
，但是参数5的类型是'uint64_t {aka long long unsigned int}'
 
 uint64_t创建; // 8字节
 time_t now = time（NULL）; 
当前时间：％li sec，％lu nanosecs，现在，msg.Created 
  

size_t可能是最高的罪犯：

sizeof的基本使用：

  warning：格式'％lu'需要类型为'long unsigned int'，
的参数，但参数4的类型为'unsigned int'
 tr_debug（pbJobs size：％lu，sizeof（pbJobs） ）; 
  

tr_debug相当于Mbed OS平台的printf。是的，我在Mbed操作系统和Linux上编译。

size_t ，假设你有一个足够现代的C库，使用％zu 。

如果你不能使用 z 修饰符（一些较旧的库不幸地不支持它），在打印时将其转换为足够宽的已知类型，然后使用适合该类型的宽度说明符：

  size_t sz = sizeof（whatever）; 
 ... 
 printf（％lu，（unsigned long）sz）; 
  

只要 超过40亿左右，即可以容纳32位。如果你在一个系统上，其中 size_t 是64位，但是 long 是32，你理论上已经得到了这个问题大小 size_t 可以容纳，但％lu 不能打印。这对你来说是一个问题，如果是这样，怎么办，取决于你。 （理想的解决方案是，如果你的程序库支持它，则返回到％zu ，这是首选解决方案，并且在32位，64位或者我猜你可以使用 unsigned long long 和％llu 。） / p>

How do you write code to compile cross-platform without warnings. For example, I don't get warnings on x64 platform, but I do on ARM (raspberry PI):

warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 5 has type ‘size_t {aka unsigned int}

Needless to say I don't want to disable warnings.

More examples and scenarios:

warning: format ‘%lu’ expects argument of type ‘long unsigned int’, 
but argument 5 has type ‘uint64_t {aka long long unsigned int}’  

uint64_t Created;       // 8 bytes
time_t now = time(NULL);
"Current time: %li sec, %lu nanosecs", now, msg.Created

size_t is probably the highest offender:

Basic use of sizeof:

warning: format ‘%lu’ expects argument of type ‘long unsigned int’, 
but argument 4 has type ‘unsigned int’
tr_debug("pbJobs size: %lu", sizeof(pbJobs));

tr_debug is equivalent of printf for Mbed OS platform. Yes, I compile on Mbed OS and Linux.

解决方案

For size_t, assuming you have a sufficiently modern C library, use %zu.

If you can't use the z modifier (some older libraries unfortunately don't support it), cast to a wide-enough known type when printing, and then use a width specifier appropriate to that type:

size_t sz = sizeof(whatever);
...
printf("%lu", (unsigned long)sz);

This works as long as you're never working with a size larger than 4 billion or so, i.e. that can fit in 32 bits. If you're on a system where size_t is 64 bits but long is 32, you've theoretically got the problem of a size which size_t can hold but %lu can't print. Whether this is a problem for you, and what to do if it is, is up to you. (The ideal solution, if your library supports it, is to go back to %zu, which is the preferred solution and doesn't have this problem in 32-bit, 64-bit, or any other sized environments. Or I guess you could use unsigned long long and %llu.)

这篇关于C printf跨平台格式没有警告的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！