里面的sprintf串c宏 [英] C macro inside string in sprintf

问题描述

我用格式化字符串复制宏。实施例在下面给出。 code给娄试图垫空字符字符串的剩余部分。

I use macro for formatted string copy. Example is given below. Code given bellow tries to pad null characters in remaining portion of string.

#include <stdio.h>

#define LEN     10
#define str(x)  #x

void main() {
    char a[LEN];
    int b = 3445;

    sprintf(a, "%-"str(LEN)"d", b);     // I want "%-10d" here
    printf("|%s|", a);
}

当我编译的gcc -Wall prog.c中它提供了以下警告。

when I compile it with gcc -Wall prog.c it gives following warnings.

warning: format ‘%LE’ expects argument of type ‘long double’, but argument 3 has type ‘int’ [-Wformat]

这意味着，宏未正确被取代。任何人可以帮助我在这里有什么错在这里。

This means that macro is not substituted properly. Can anybody help me here what is wrong here.

推荐答案

您不得不评估参数 STR 再一次看到10里面的字符串

You'd have to evaluate the argument to str once more to see the 10 inside the string

#define LEN     10
#define str_(x)  #x
#define str(x)  str_(x)

你的方式做到了，参数为 STR 直接stringyfied，因此 LEN 抵达格式

the way you did it, the argument to str is stringyfied directly, thus the LEN arrived in the format.

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