函数在C中分配了不正确的浮点值 [英] Function assigns incorrect float value in C

问题描述

我试图返回一个浮点值并将其分配给一个浮点变量，但是新的浮点值与返回的值不同.

I am trying to return a float value and assign it to a float variable, but the value of the new float is different from the returned one.

float getVoltageReading() {
    return 1.2f;
}


void updateUIReadings(uint8_t menuID) {
    float integerReading = getVoltageReading(); // digital voltage
}

在调试器中，我看到getVoltageReading返回 1.2 ，但是将integerReading分配为 1.06703091e + 009

In debugger I see that getVoltageReading return 1.2, but the integerReading is assigned to be 1.06703091e+009

那是为什么?

推荐答案

您正在调用 getVoltageReading 函数，而该函数在范围内没有活动的原型，这意味着它假定将返回int .从问题的组织方式来看，它看起来是在范围内，但我可以向您保证它不在范围内.

You are calling the getVoltageReading function without an active prototype in scope, which means it is assuming that it will return an int. It looks like, from the way your question is organised, that it is in scope, but I can assure you it's not.

通过以下两个文件，您可以看到 testprog1.c :

You can see that with the following two files, testprog1.c:

#include <stdio.h>

//float getVoltageReading(void);

int main(void) {
    float integerReading = getVoltageReading ();
    printf("%e\n", integerReading);
    return 0;
}

和 testprog2.c :

float getVoltageReading(void) {
    return 1.2f;
}

将它们编译并链接在一起后，输出为:

When these are compiled and linked together, the output is:

1.067031e+09

因为从 getVoltageReading()返回的浮点值被解释为 int .如果您在 testprog1.c 中取消注释原型，它会正常工作，因为它将float值解释为 float :

because the float value being returned from getVoltageReading() is being interpreted as an int. If you uncomment the prototype in testprog1.c, it works fine because it interprets the float value as a float:

1.200000e+00

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