Type Mismatch: Integer to Character

C/C++

Abstract

函数将返回转换为 int 的 unsigned char，但返回值将赋给 char 类型。

Explanation

当转换为整数的不带符号的字符赋给带符号的字符时，可能无法从 EOF 区别其值。

示例 1：以下代码会读取一个字符，并将其与 EOF 进行比较。


char c;

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

在这种情况下，来自 getchar() 的返回值将转换为 char 并与 EOF（一个 int）进行比较。假设 c 是一个带符号的 8 位值，EOF 是一个带符号的 32 位值，那么如果 getchar() 返回由 0xFF 表示的字符，则与 EOF 相比，c 的值将是 0xFFFFFFFF 的符号扩展。由于 EOF 通常定义为 -1 (0xFFFFFFFF)，因此该循环将错误地终止。

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