C++变量定义最佳实践-优快云博客

这使得它似乎有点更清楚，价值5是只被分配到变量B。

zhè这shǐ使de得tā它sì似hū乎yǒu有diǎn点gèng更qīng清chǔ楚，jià价zhí值 5shì是zhǐ只bèi被fēn分pèi配dào到biàn变liàng量 B 。

Because defining multiple variables on a single line AND initializing them is a recipe for mistakes, we recommend that you only define multiple variables on a line if you’re not initializing any of them.

因为定义多个变量在一个单一的线和初始化是一方的错误，我们建议您只定义多个变量对线如果你没有初始化任何人。

yīn因wèi为dìng定yì义duō多gè个biàn变liàng量zài在yī一gè个dān单yī一de的xiàn线hé和chū初shǐ始huà化shì是yī一fāng方de的cuò错wù误，wǒ我men们jiàn建yì议nín您zhǐ只dìng定yì义duō多gè个biàn变liàng量duì对xiàn线rú如guǒ果nǐ你méi没yǒu有chū初shǐ始huà化rèn任hé何rén人。

Rule: Avoid defining multiple variables on a single line if initializing any of them.

规则：避免定义多个变量在一个单一的线如果初始化任何人。

guī规zé则：bì避miǎn免dìng定yì义duō多gè个biàn变liàng量zài在yī一gè个dān单yī一de的xiàn线rú如guǒ果chū初shǐ始huà化rèn任hé何rén人。

Where to define variables

定义变量的地方

dìng定yì义biàn变liàng量de的dì地fāng方

Older C compilers forced users to define all of the variables in a function at the top of the function:

老年编译器强制用户定义函数中的所有变量的函数的顶部的功能：

int main()
{
    // all variable up top
    int x;
    int y;
 
    // then code
    using namespace std;
    cout << "Enter a number: ";
    cin >> x;
 
    cout << "Enter another number: ";
    cin >> y;
 
    cout << "The sum is: " << x + y << endl;
    return 0;
}

这种风格现在已经过时。C++编译器不需要所有的变量都是在函数上定义。适当的C++风格定义的变量，变量的第一个接近的使用可能：

int main()
{
    using namespace std;
 
    cout << "Enter a number: ";
    int x; // we need x on the next line, so we'll declare it here, as close to its first use as possible.
    cin >> x; // first use of x
 
    cout << "Enter another number: ";
    int y; // we don't need y until now, so it gets declared here
    cin >> y; // first use of y
 
    cout << "The sum is: " << x + y << endl;
    return 0;
}

这有相当多的优势。

zhè这yǒu有xiāng相dāng当duō多de的yōu优shì势。

First, variables that are defined only when needed are given context by the statements around them. If x were defined at the top of the function, we would have no idea what it was used for until we scanned the function and found where it was used. Defining x amongst a bunch of input/output statements helps make it obvious that this variable is being used for input and/or output.

首先，只有在需要时才定义的变量是在它们的语句中给出的。如果被定义在功能的顶部，我们将不知道它是什么，直到我们扫描的功能，并发现它被使用。定义一堆输入/输出语句之间的定义有助于使其明显的是，这个变量被用于输入和/或输出。

shǒu首xiān先，zhǐ只yǒu有zài在xū需yào要shí时cái才dìng定yì义de的biàn变liàng量shì是zài在tā它men们de的yǔ语jù句zhōng中jǐ给chū出de的。rú如guǒ果bèi被dìng定yì义zài在gōng功néng能de的dǐng顶bù部，wǒ我men们jiāng将bù不zhī知dao道tā它shì是shén什me么，zhí直dào到wǒ我men们sǎo扫miáo描de的gōng功néng能，bìng并fā发xiàn现tā它bèi被shǐ使yòng用。dìng定yì义yī一duī堆shū输rù入 /shū输chū出yǔ语jù句zhī之jiān间de的dìng定yì义yǒu有zhù助yú于shǐ使qí其míng明xiǎn显de的shì是，zhè这ge个biàn变liàng量bèi被yòng用yú于shū输rù入hé和 /huò或shū输chū出。

Second, defining a variable only where it is needed tells us that this variable does not affect anything above it, making our program easier to understand and requiring less scrolling.

其次，定义一个变量，只有在它的需要告诉我们，这个变量不影响上面的任何东西，使我们的程序更容易理解，需要较少的滚动。

qí其cì次，dìng定yì义yī一gè个biàn变liàng量，zhǐ只yǒu有zài在tā它de的xū需yào要gào告sù诉wǒ我men们，zhè这ge个biàn变liàng量bù不yǐng影xiǎng响shàng上miàn面de的rèn任hé何dōng东xi西，shǐ使wǒ我men们de的chéng程xù序gèng更róng容yì易lǐ理jiě解，xū需yào要jiào较shǎo少de的gǔn滚dòng动。

Finally, it reduces the likelihood of inadvertently leaving a variable uninitialized, because we can define and then immediately initialize it with the value we want it to have.

最后，它减少了无意中留下一个变量未初始化的可能性，因为我们可以定义然后立即初始化它的价值我们要有。

zuì最hòu后，tā它jiǎn减shǎo少le了wú无yì意zhōng中liú留xià下yī一gè个biàn变liàng量wèi未chū初shǐ始huà化de的kě可néng能xìng性，yīn因wèi为wǒ我men们kě可yǐ以dìng定yì义rán然hòu后lì立jí即chū初shǐ始huà化tā它de的jià价zhí值wǒ我men们yào要yǒu有。