我正在阅读《C++ 如何编程》第 9 版,尝试学习 C++,并尝试使用第 7 章中的骑士问题进行练习。
根据输出中的“64”,代码显然存在某种逻辑错误(我将自行修复),但在执行此操作之前,我一直在理解以及如何处理编译器警告。
我已将 board 声明为 unsigned int 的二维数组,因为它只能包含值 0-7。同样,出于同样的原因,我已将 for 循环中的变量声明为 unsigned int。
我在 stackoverflow 上读过有关此问题的回复,但它们很快就超出了我的理解范围。
#include <iostream>
#include <array>
#include <iomanip>
using namespace std;
void printArray(const array< array< unsigned int, 8 >, 8 >);
int main() {
array< array< unsigned int, 8 >, 8 > board = {};
array< int, 8 > horizontal = {{ 2, 1, -1, -2, -2, -1, 1, 2 }};
array< int, 8 > vertical = {{ -1, -2, -2, -1, 1, 2, 2, 1 }};
unsigned int currentRow = 0;
unsigned int currentCol = 0;
for (unsigned int i = 0; i < 64; i++) {
board[currentRow][currentCol] = i + 1;
for (unsigned int j = 0; j < 8; j++) {
if (currentRow + horizontal[j] >= 0 &&
currentRow + horizontal[j] < 8 &&
currentCol + vertical[j] >= 0 &&
currentCol + vertical[j] < 8 &&
board[currentRow + horizontal[j]][currentCol + vertical[j]] == 0
) {
currentRow = currentRow + horizontal[j];
currentCol = currentCol + vertical[j];
break;
}
}
}
printArray(board);
}
void printArray(const array< array< unsigned int, 8 >, 8 > myBoard) {
for ( unsigned int i = 0; i < 8; i++) {
for ( unsigned int j = 0; j < 8; j++) {
cout << '[' << setw(2) << setfill('0') << myBoard[i][j] << "] ";
}
cout << endl;
}
}
输出:
~/Programming/cpp/knight => make
rm -fr build/*
clang++ -std=c++11 -stdlib=libc++ -Weverything -Wno-c++98-compat src/main.cpp -o build/main -Isrc/
src/main.cpp:18:24: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
if (currentRow + horizontal[j] >= 0 &&
~ ^~~~~~~~~~~~~
src/main.cpp:18:38: warning: comparison of unsigned expression >= 0 is always true [-Wtautological-compare]
if (currentRow + horizontal[j] >= 0 &&
~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~
src/main.cpp:19:22: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
currentRow + horizontal[j] < 8 &&
~ ^~~~~~~~~~~~~
src/main.cpp:20:22: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
currentCol + vertical[j] >= 0 &&
~ ^~~~~~~~~~~
src/main.cpp:20:34: warning: comparison of unsigned expression >= 0 is always true [-Wtautological-compare]
currentCol + vertical[j] >= 0 &&
~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~
src/main.cpp:21:22: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
currentCol + vertical[j] < 8 &&
~ ^~~~~~~~~~~
src/main.cpp:22:28: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
board[currentRow + horizontal[j]][currentCol + vertical[j]] == 0
~ ^~~~~~~~~~~~~
src/main.cpp:22:56: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
board[currentRow + horizontal[j]][currentCol + vertical[j]] == 0
~ ^~~~~~~~~~~
src/main.cpp:24:35: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
currentRow = currentRow + horizontal[j];
~ ^~~~~~~~~~~~~
src/main.cpp:25:35: warning: implicit conversion changes signedness: 'value_type' (aka 'int') to 'unsigned int' [-Wsign-conversion]
currentCol = currentCol + vertical[j];
~ ^~~~~~~~~~~
10 warnings generated.
./build/main
[01] [24] [09] [00] [00] [26] [37] [00]
[10] [41] [02] [25] [36] [00] [00] [27]
[23] [08] [11] [40] [21] [38] [00] [00]
[64] [03] [22] [35] [00] [00] [28] [00]
[07] [12] [05] [20] [39] [34] [00] [00]
[04] [17] [14] [31] [00] [29] [00] [00]
[13] [06] [19] [16] [33] [00] [00] [00]
[18] [15] [32] [00] [30] [00] [00] [00]
最佳答案
编译器告诉你,当你编写时
currentRow + horizontal[j] >= 0
您要添加一个signed int
和一个unsigned int
,因此signed int
会转换为unsigned int
,因此总和的结果是一个 unsigned int
。 unsigned int
始终大于或等于零。
所以这个测试总是true
,这可能不完全是你想要的。
同样的问题
currentCol + vertical[j] >= 0
更一般地说,对于有符号
/无符号
值的每个总和。
一种选择是将 currentRow
和 currentCol
定义为 (signed
) int
。
否则,您可以在将unsigned
值添加到signed
值时适本地转换它们
int{currentRow} + horizontal[j] >= 0
关于c++ - 如何修复隐式转换警告?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/48648942/