How to solve C++ syntax error: 'expected initializer before '<' token'?

How to solve C syntax error: 'expected initializer before '<' token'?

In C programming, various errors are often encountered. One of the common errors is "expected initializer before '<' token". This error usually occurs when using template classes or template functions, and you need to pay attention to some specific syntax details. In this article, we will discuss the causes of this error and how to fix it.

First, let’s look at a code example to better understand this error:

template <typename T>
void PrintVector(vector<T> vec) {
    for (const auto& elem : vec) {
        cout << elem << " ";
    }
    cout << endl;
}

int main() {
    vector<int> myVector = {1, 2, 3, 4, 5};
    PrintVector<int>(myVector);
    return 0;
}

In the above code, we define a template function PrintVector that accepts a vector object and Print its elements. In the main function, we create a vector object containing integers and pass it to the PrintVector function. However, when we try to compile this code, we get the following error message: "expected initializer before '<' token".

The reason for this error is that the compiler does not recognize the "<" symbol. This is because the C compiler by default interprets "<" as a comparison operator and not as part of the template parameter list. Therefore, we need a way to tell the compiler that "<" is part of a template parameter list.

It is very simple to solve this error. We only need to add the keyword "template" before the "<" symbol after the template function. The modified code is as follows:

template <typename T>
void PrintVector(vector<T> vec) {
    for (const auto& elem : vec) {
        cout << elem << " ";
    }
    cout << endl;
}

int main() {
    vector<int> myVector = {1, 2, 3, 4, 5};
    PrintVector<int>(myVector);
    return 0;
}

Now, we have added the "template" keyword to tell the compiler that "<" is part of a template parameter list. This allows the compiler to correctly identify template types in your code.

After correcting the error, recompile the code and you will get the output we expect. This is how to solve the C syntax error "expected initializer before '<' token".

To summarize, when you encounter the error message "expected initializer before '<' token" in C programming, it may be caused by the template type not being specified correctly. This error can be resolved by adding the "template" keyword before the template function or template class, and ensuring that the "<" symbol is correctly interpreted as part of the template parameter list. I hope this article can help readers solve these common C syntax errors.

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