MBED OS 6 无法打印浮点

修改方式： 在项目根目录创建mbed_app.json

{
    "target_overrides": {
        "*": {
             "target.printf_lib": "std"
        }
    }
}

将target.printf_lib的值覆盖为std（即不使用minimal-printf，使用标准库）

或者

{
    "target_overrides": {
        "*": {
            "target.printf_lib": "minimal-printf",
            "platform.minimal-printf-enable-floating-point": true,
            "platform.minimal-printf-set-floating-point-max-decimals": 6,
            "platform.minimal-printf-enable-64-bit": false
        }
    }
}

启用minimal-printf对浮点数输出的功能。

原因就是MBED OS 6 默认使用minimal-printf

minimal-printf是为了减少资源占用，提供的替代printf的库。支持以下的格式化输出，其中浮点相关是默认disabled：

• %d: signed integer [h, hh, (none), l, ll, z, j, t].
• %i: signed integer [h, hh, (none), l, ll, z, j, t].
• %u: unsigned integer [h, hh, (none), l, ll, z, j, t].
• %x: unsigned integer [h, hh, (none), l, ll, z, j, t], printed as hexadecimal number (e.g., ff).
• %X: unsigned integer [h, hh, (none), l, ll, z, j, t], printed as hexadecimal number (e.g., FF).
• %f: floating point (disabled by default).
• %F: floating point (disabled by default, treated as %f).
• %g: floating point (disabled by default, treated as %f).
• %G: floating point (disabled by default, treated as %f).
• %c: character.
• %s: string.
• %p: pointer (e.g. 0x00123456).