invalid array assignment c

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  Invalid array assignment

Declaration

A C string (also known as a null-terminated string is usually declared as an array of char . However, an array of char is not by itself a C string. A valid C string requires the presence of a terminating "null character" (a character with ASCII value 0, usually represented by the character literal '\0' ).

Since char is a built-in data type, no header file needs to be included to create a C string. The C library header file <cstring> contains a number of utility functions that operate on C strings.

Here are some examples of declaring C strings as arrays of char :

It is also possible to declare a C string as a pointer to a char :

This creates an unnamed character array just large enough to hold the string (including the null character) and places the address of the first element of the array in the char pointer s3 . This is a somewhat advanced method of manipulating C strings that should probably be avoided by inexperienced programmers who don't understand pointers yet. If used improperly, it can easily result in corrupted program memory or runtime errors.

Representation in Memory

Here is another example of declaring a C string:

The following diagram shows how the string name is represented in memory:

The individual characters that make up the string are stored in the elements of the array. The string is terminated by a null character. Array elements after the null character are not part of the string, and their contents are irrelevant.

A "null string" or "empty string" is a string with a null character as its first character:

The length of a null string is 0.

What about a C string declared as a char pointer?

This declaration creates an unnamed character array just large enough to hold the string "Karen" (including room for the null character) and places the address of the first element of the array in the char pointer name :

Subscripting

Like any other array, the subscript operator may be used to access the individual characters of a C++ string:

Since the name of a C string is converted to a pointer to a char when used in a value context, you can also use pointer notation to access the characters of the string:

String Length

You can obtain the length of a C string using the C library function strlen() . This function takes a character pointer that points to a C string as an argument. It returns the data type size_t (a data type defined as some form of unsigned integer), the number of valid characters in the string (not including the null character).

String Comparison

Comparing C strings using the relational operators == , != , > , < , >= , and <= does not work correctly, since the array names will be converted to pointers. For example, the expression

actually compares the addresses of the first elements of the arrays s1 and s2 , not their contents. Since those addresses are different, the relational expression is always false.

To compare the contents of two C strings, you should use the C library function strcmp() . This function takes two pointers to C strings as arguments, either or both of which can be string literals. It returns an integer less than, equal to, or greater than zero if the first argument is found, respectively, to be less than, to match, or be greater than the second argument.

The strcmp() function can be used to implement various relational expressions:

A character array (including a C string) can not have a new value assigned to it after it is declared.

To change the contents of a character array, use the C library function strcpy() . This function takes two arguments: 1) a pointer to a destination array of characters that is large enough to hold the entire copied string (including the null character), and 2) a pointer to a valid C string or a string literal. The function returns a pointer to the destination array, although this return value is frequently ignored.

If the string specified by the second argument is larger than the character array specified by the first argument, the string will overflow the array, corrupting memory or causing a runtime error.

Input and Output

The stream extraction operator >> may be used to read data into a character array as a C string. If the data read contains more characters than the array can hold, the string will overflow the array.

The stream insertion operator << may be used to print a C string or string literal.

Concatenation

The C library function strcat() can be used to concatenate C strings. This function takes two arguments: 1) a pointer to a destination character array that contains a valid C string, and 2) a pointer to a valid C string or string literal. The function returns a pointer to the destination array, although this return value is frequently ignored.

The destination array must be large enough to hold the combined strings (including the null character). If it is not, the array will overflow.

Passing and returning

Regardless of how a C string is declared, when you pass the string to a function or return it from a function, the data type of the string can be specified as either char[] (array of char ) or char* (pointer to char ). In both cases, the string is passed or returned by address .

A string literal like "hello" is considered a constant C string, and typically has its data type specified as const char* (pointer to a char constant).

C++ 数组分配错误 : invalid array assignment

标签 c++ c arrays

我不是 C++ 程序员，所以我需要一些有关数组的帮助。 我需要将一个字符数组分配给某个结构，例如

我得到 error: invalid array assignment

如果 mStr.message 和 hello 具有相同的数据类型，为什么它不起作用？

因为您不能分配给数组——它们不是可修改的左值。使用 strcpy:

正如 Kedar 已经指出的那样，您还写出了数组的末尾。

关于C++ 数组分配错误 : invalid array assignment，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/4118732/

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char array help

I am fairly new to coding and arduino. I am trying to have arduino write "On" or "Off" to a char variable depending on state of digital out pin. I keep getting invalid array assignment. Can someone explain to me why my code doesn't work? Thanks in advance

Arrays are groups of logically linked memory addresses. You can not assign one group of memory addresses to another group of memory addresses.

You can copy what's in one group of logically linked memory addresses (one array) to another in several ways. All depend on knowing how much memory is to be copied, to where.

Your arrays are dynamically sized, although they all end up the same size (4 chars long).

There is also the memcpy function and strcpy functions that can be used. How to use them is left as an exercise in RTFM for you.

Thanks for the reply, I will give it a try. Even though the arrays are dynamically sized i made them all 4 chars long since i got some earlier messages about arrays not being the same size.

Just so I understand your code. basically its replacing each char of the 4 char array one by one right?

Yes. The strcpy and memcpy functions implement the loops inside the functions.

Thanks I will look at those functions as well.

Thanks for the help.

@PaulS : Couple of things here:

Arrays are groups of logically linked memory addresses.

I think you may be confusing arrays (collections of data items with sequential memory addresses) with lists (groups of linked memory addresses).

You can not assign one group of memory addresses to another group of memory addresses.

Not strictly true; structures can be directly assigned, without resorting to "memcpy" or "for" loops.

For the purposes of illustrating why the "array = array" assignment worked, I think my explanation was OK. I was thinking sequential when I typed linked. I though about changing it, but, I decided that the difference wasn't that important.

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ProgrammerAH

Programmer guide, tips and tutorial, c++ bug: [error] invalid array assignment.

C++BUG: [Error] invalid array assignment

1. Introduction2. The difference between the return value of memcpy() function prototype function header file and strcpy

1. Introduction

When using array to assign value to array, the above bug will appear. The general chestnut is as follows:

The purpose is to store the data in the structure array object SS [J], but this assignment will report an error.

2. memcpy()

Function prototype

The data of consecutive n bytes with SRC pointing address as the starting address is copied into the space with destination pointing address as the starting address.

Header file

The use of # include & lt; string. H & gt;;

Both # include & lt; CString & gt; and # include & lt; string. H & gt; can be used in C + +

Return value

Function returns a pointer to dest.

The difference from strcpy

1. Compared with strcpy, memcpy does not end when it encounters’ \ 0 ‘, but will copy n bytes. Therefore, we need to pay special attention to memory overflow. 2. Memcpy is used to copy memory. You can use it to copy objects of any data type, and you can specify the length of the data to be copied. Note that source and destination are not necessarily arrays, and any read-write space can be used; however, strcpy can only copy strings, and it ends copying when it encounters’ \ 0 ‘.

For 2D arrays

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C/C++BUG: [Error] invalid array assignment

C++ array assign error: invalid array assignment

Because you can’t assign to arrays — they’re not modifiable l-values. Use strcpy:

And you’re also writing off the end of your array, as Kedar already pointed out.

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[解決済み】C++の配列の割り当てエラー：無効な配列の割り当て

私はC++プログラマーではないので、配列について手助けが必要です。 私は文字列の配列をある構造体に代入する必要があります。

私は error: invalid array assignment

なぜうまくいかないかというと、もし mStr.message と hello は同じデータ型ですか？

どのように解決するのですか？

配列は変更可能なL値ではないので、代入はできません。strcpyを使ってください。

また、Kedarがすでに指摘しているように、配列の末尾を書き換えていますね。

[解決済み】C++エラーです。"配列は中括弧で囲まれたイニシャライザーで初期化する必要がある"

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