Type Mismatch: Integer to Character

C/C++

Abstract

函數會傳回轉換為 int 的 unsigned char，但傳回值會指定為 char 類型。

Explanation

當轉換為整數的無符號字元指派給有符號的字元，其值可能會與 EOF 無法區分。

範例 1：以下程式碼讀取一個字元，並將其與 EOF 做比較。


char c;

while ( (c = getchar()) != '\n' && c != EOF ) {
  ...
}

在此案例中，getchar() 的傳回值會轉換為 char，並與 EOF (int) 做比較。假設 c 是 8 位元有號值，而 EOF 是 32 位元有號值，那麼若 getchar() 傳回以 0xFF 表示的字元，則在與 EOF 比較時，c 值的正負數符號將會延伸至 0xFFFFFFFF。由於 EOF 通常會定義為-1 (0xFFFFFFFF)，因此迴圈會錯誤地終止。

References

[1] Distinguish between characters read from a file and EOF or WEOF CERT

[2] Standards Mapping - Common Weakness Enumeration CWE ID 192

[3] Standards Mapping - Motor Industry Software Reliability Association (MISRA) C Guidelines 2012 Rule 10.3

[4] Standards Mapping - Motor Industry Software Reliability Association (MISRA) C Guidelines 2023 Rule 7.5, Rule 7.6, Rule 10.3

[5] Standards Mapping - Motor Industry Software Reliability Association (MISRA) C++ Guidelines 2008 Rule 5-0-3

[6] Standards Mapping - Motor Industry Software Reliability Association (MISRA) C++ Guidelines 2023 Rule 7.0.5, Rule 7.0.6

[7] Standards Mapping - Payment Card Industry Data Security Standard Version 3.0 Requirement 6.5.6

[8] Standards Mapping - Payment Card Industry Data Security Standard Version 3.1 Requirement 6.5.6

[9] Standards Mapping - Payment Card Industry Data Security Standard Version 3.2 Requirement 6.5.6

[10] Standards Mapping - Payment Card Industry Data Security Standard Version 3.2.1 Requirement 6.5.6

[11] Standards Mapping - Payment Card Industry Data Security Standard Version 4.0 Requirement 6.2.4

[12] Standards Mapping - Payment Card Industry Data Security Standard Version 4.0.1 Requirement 6.2.4

[13] Standards Mapping - Payment Card Industry Software Security Framework 1.0 Control Objective 4.2 - Critical Asset Protection

[14] Standards Mapping - Payment Card Industry Software Security Framework 1.1 Control Objective 4.2 - Critical Asset Protection

[15] Standards Mapping - Payment Card Industry Software Security Framework 1.2 Control Objective 4.2 - Critical Asset Protection

[16] Standards Mapping - Security Technical Implementation Guide Version 3.1 APP3550 CAT I

[17] Standards Mapping - Security Technical Implementation Guide Version 3.4 APP3550 CAT I

[18] Standards Mapping - Security Technical Implementation Guide Version 3.5 APP3550 CAT I

[19] Standards Mapping - Security Technical Implementation Guide Version 3.6 APP3550 CAT I

[20] Standards Mapping - Security Technical Implementation Guide Version 3.7 APP3550 CAT I

[21] Standards Mapping - Security Technical Implementation Guide Version 3.9 APP3550 CAT I

[22] Standards Mapping - Security Technical Implementation Guide Version 3.10 APP3550 CAT I

desc.structural.cpp.type_mismatch_integer_to_character