What is the return value of the C language function

The return value of the C language function is the value returned to the caller after the function is calculated. It can be of multiple data types, or even does not return (void). The return value not only passes the calculation result, but also represents the function execution status. Choosing the appropriate return value type can improve code readability and avoid potential problems.

C function returns value? This question is awesome! It looks simple on the surface, but in fact there are many tricks inside. Simply put, the return value of the function is the value returned to the caller after the function is calculated. But the meaning of "value" can be broad. It can be an integer, a floating point number, a character, a pointer, or even a structure or a union, or even returns nothing, that is, it returns void .

Think about it, if there is no return value, the function becomes a one-way "black box". You can only stuff things into it, but you don't know what the result is after it is processed. This is a big taboo in programming! With the return value, the function has a feedback mechanism, which makes the program's process clearer and easier to debug.

Take a chestnut, a function that calculates the sum of two numbers:

 <code class="c">int add(int a, int b) { return ab; }</code>

This function takes two integers a and b as parameters, calculates their sum, and then returns the result - an integer - to the caller using the return statement. The caller can receive this return value with a variable:

 <code class="c">int sum = add(5, 3); // sum 现在等于8</code>

You see, the return value makes the output of the function controllable and the program logic is clearer.

But the return value is not as simple as passing the calculation result. It can also be used to represent the state of function execution. For example, a file read function can return the read data if the read is successful; if it fails, it can return a specific value (such as -1) to indicate an error. In this way, the caller can judge whether the function is executed successfully based on the return value and take corresponding measures.

 <code class="c">int readFile(char *filename, char *buffer, int bufferSize) { FILE *fp = fopen(filename, "r"); if (fp == NULL) return -1; // 文件打开失败int bytesRead = fread(buffer, 1, bufferSize, fp); fclose(fp); if (bytesRead </code>

Here, the return value assumes the role of "status code", which can better reflect the execution details of the function than the simple true / false . This is very important when handling errors and exceptions.

Going deeper, the type of the return value is closely related to the purpose of the function. Choosing the appropriate return value type can not only improve the readability of the code, but also avoid some potential problems. For example, if a function needs to return a large integer and you use int type, it may cause data overflow. At this time, you need to consider using long long or even unsigned long long to ensure the integrity of your data.

There are some points to note: return statement will immediately terminate the execution of the function, so be careful to place return statement to avoid logical errors. Additionally, for some complex functions, multiple values ​​may be required. At this time, you can consider using pointers, structures, or unions as return values, or passing multiple values ​​through output parameters.

In short, the return value of C functions seems simple, but contains a lot of skills and details. Understanding and proficient in using return values ​​is the key to writing high-quality C code. Don't underestimate this small return value, it is a bridge between functions and callers and the cornerstone of program logic.

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