有没有办法直接在函数参数中格式化字符串而不是使用临时字符串? [英] Is there a way to format a string directly within a functions arguments instead of using a temporary string?

问题描述

我有一个接受字符串(字符数组)作为参数的函数.

I have a function that accepts a string (char array) as its argument.

void enterString(char * my_string);

在使用这个函数时，我经常发现自己想要输入格式化的字符串.我使用 sprintf 来做到这一点.但是，每次都必须创建一个临时字符串有点烦人:

When using this function, I often find myself wanting to input formatted strings. I use sprintf to do this. However, It's kind of annoying that I have to create a temporary string every time:

char temp_str[100];
sprintf(temp_str, "My lucky number = %d", 11);
enterString(temp_str);

有什么方法可以在函数参数中直接格式化字符串，这样我就不必每次都创建一个临时字符串?类似的东西:

Is there any way to directly format a string within a functions arguments so I don't have to create a temporary string every time? Something like:

enterString("My lucky number = %d", 11);

谢谢

推荐答案

您不能在 C 中执行此操作(与 Python 等其他语言不同，它们具有使用 % 运算符或 str.format 函数).

You cannot do this in C (unlike other languages like python which have built-in formatting for string with the % operator or str.format function).

但是由于您的方法看起来像是要打印带有可变参数的格式化消息，您可以使用可以接受 va_list 的 vfprintf参数，因此您可以将可变参数传递给内部函数.

But since your approach looks like you want to print a formatted message with variable arguments, you could use vfprintf that can accept a va_list argument, so you can transfer your variable arguments to your inner function.

#include <stdio.h>
#include <stdarg.h>

void enterString(const char *format,...)
{

  va_list argptr;
  va_start(argptr, format);
  vfprintf(stdout, format, argptr);
  va_end(argptr);
  // rest of the processing here
}

int main()
{
   enterString("My lucky number = %d", 11);
   return 0;
}

与 printf 相比，这并没有带来太多，但是现在你有了这个，您可以添加对详细"模式的检查、登录到文件、打印前缀、日期、...在消息之前等...

This doesn't bring a lot compared to printf, but now that you have this, you can add a check for "verbose" mode, log to a file, print a prefix, date, ... before the message, etc...

我在 musashi 680x0 模拟器(在 m68kfpu.c 中)中找到了这个确切的代码

I found this exact code in the musashi 680x0 emulator (in m68kfpu.c)

static void fatalerror(char *format, ...) {
  va_list ap;
  va_start(ap,format);
  vfprintf(stderr,format,ap);
  va_end(ap);
  exit(1);
}

(我不得不修复代码中错误的fprintf，但除此之外，我们看到了一个直接的应用程序:该函数用于打印变量格式的错误消息，然后退出操作系统)

(I had to fix the wrong fprintf that was in the code, but apart from that, we see a direct application: this function is used to print a variable formatted error message, then quit to the operating system)

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