Article Tags
Article Tags
How to format output in C ? (std::cout precision settings)
Use std::fixed with std::setprecision to fix the number of decimal places; std::fixed disables scientific notation, and setprecision(n) represents n digits after the decimal point under fixed; #include is required; to avoid contaminating the global state, flags and precision should be saved and restored, or formatted in isolation with ostringstream.
Mar 06, 2026 am 02:34 AM
How to convert char array to string in C ? (Type conversion)
The most direct way to convert a char array to a string using the std::string constructor is to hand over a continuous C-style string (ending with '\0') to std::string for management. The safest way is to call its constructor: chaarr[]="hello";std::strings(arr); This line of code will automatically stop when it reads '\0', and there is no need to manually pass the length. But the premise is that arr does end with '\0' - if it is an uninitialized stack array, or a fragment cut out from binary data, it may read memory out of bounds. If the array does not contain '\0' (for example, you only used the first 5 characters
Mar 06, 2026 am 02:31 AM
How to parse JSON data in C ? (Library integration)
nlohmann/json is the easiest to parse JSON. It only requires the introduction of header files and using statements. It supports direct parse strings, safe nested values, and UTF-8 encoding processing; it needs to prevent parse_error exceptions, BOM/ANSI encoding issues, and large file memory usage.
Mar 06, 2026 am 02:29 AM
How to concatenate strings in C ? (Append methods)
Using operator = to append a string is most straightforward. Most of the time you just want to add one string to the end of another, and operator = is the most natural choice. It modifies the original string, does not generate temporary objects, has good performance and clear semantics. A common mistake is to mistakenly think that it returns a new string - in fact, it returns a reference to the original object and supports chain calls, but don't use it to assign a value to a new variable and expect to get a copy. std::strings="hello";s ="world";→Correct, s becomes "helloworld" autot=s ="!"→t and s are the same
Mar 06, 2026 am 02:09 AM
How to sort a vector in C ? (std::sort algorithm)
std::sort defaults to ascending order because of the use of operator
Mar 06, 2026 am 02:08 AM
How to use std::move in C ? (Move semantics explained)
When should you use std::move? Only use it when you explicitly want to "give up ownership of the current object" and transfer resources to another object. It is not a performance optimization switch, nor is it a panacea for "making the code faster" - using it incorrectly can lead to dangling, repeated releases or compilation failures. Typical scenarios: std::vector elements are moved and inserted, functions return local objects, and move constructors/assignment operators are implemented. Common error phenomena: after std::move, continue to access the original object (such as taking .size() or calling a non-noexcept member function), and the result is undefined; or std::move repeatedly for const objects, literals, and rvalue reference parameters returned by functions. In fact,
Mar 06, 2026 am 01:37 AM
How to delete an element from an array in C ? (Vector erase method)
When vector::erase deletes a single element, the iterator will become invalid. After calling vec.erase(it), all iterators, references, and pointers at the deleted position and after will become invalid. A common mistake is to continue to use the original iterator to increment after deletion: it. As a result, a wild address is accessed or the next element is skipped. Correct approach: Use the new iterator returned by erase() to continue traversing. It points to the next position of the deleted element. Only delete an element at a known position (such as the first matching item). Just use vec.erase(find(...)) directly. There is no need to manually maintain the iterator. If you want to delete multiple elements that meet the conditions, you must update the iterator with the return value: it=vec.erase(it).
Mar 06, 2026 am 01:31 AM
How to use std::optional in C ? (Handling missing values)
std::optional is a type safety tool used to clearly express that the value may not exist. It is suitable for scenarios where the function return result may be invalid (such as division by zero, parsing failure), rather than replacing pointers or managing heap memory; naked adjustment of value() should be avoided, and value_or() or has_value() should be used first to check. Explicit initialization is recommended during construction, and std::nullopt is used for clearing.
Mar 05, 2026 am 02:50 AM
How to link external libraries in C ? (Static vs Dynamic linking)
The static link library must be placed after the source file, and the dynamic library needs to be configured with a runtime path or a static link standard library. When the ABI does not match, you should avoid upgrading the system library and use -static-libstdc or old mirror compilation instead.
Mar 05, 2026 am 02:46 AM
How to use the auto keyword in C ? (Type inference)
When it is time to use auto instead of handwritten types: the expression type is known and the type name is lengthy (such as iterators, lambda return values, template nested types), which can avoid spelling errors and improve maintainability; except for function parameters, class member variables and interfaces that require clear semantics.
Mar 05, 2026 am 02:43 AM
How to reverse a string in C ? (std::reverse example)
std::reverse directly reverses the container in place and returns void without generating a new copy; you need to copy it first and then call it or use std::string(s.rbegin(), s.rend()) to construct a new string. Pay attention to the iterator type, header file and read-only memory restrictions.
Mar 05, 2026 am 02:32 AM
How to initialize a vector in C ? (std::vector syntax)
It is safest to use the std::vector constructor directly. Do not write push_back by hand, and do not rely on resize after default construction. For most initialization requirements, the std::vector constructor can be completed in one step. It can automatically allocate memory, call element constructors, and avoid copy overhead caused by subsequent expansion. Empty container: std::vectorv; or std::vectorv{}; Specified size (value initialization): std::vectorv(10);→10 0s specify the size Initial value: std::vectorv(10,42);→10 42 from array/initialization
Mar 05, 2026 am 02:28 AM
How to calculate the factorial of a number in C ? (Recursion logic)
Recursive factorial calculations most often crash due to incorrect handling of boundaries. For example, when n==0 or n==1, the recursion continues without returning 1, resulting in infinite calls and stack overflows; C does not automatically truncate, and basecase must be written explicitly: if(n
Mar 05, 2026 am 02:24 AM
How to write to a CSV file in C ? (File handling)
It is not difficult to write CSV directly using std::ofstream. However, when opened in Excel, the files written by most people will be misaligned, garbled, or all crowded into one grid. The core issue is not "how to write", but "how to write so that the spreadsheet software can recognize it". CSV is not a plain text concatenation. It has implicit rules: fields are separated by , and the end of each line must be \n (\r\n is recommended under Windows). Empty fields or fields containing commas/newlines must be wrapped in double quotes. Don't go out directly
Mar 05, 2026 am 02:11 AM
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