C++ 中 abs() 的错误 [英] Error with abs() in c++

问题描述

在此代码的第 35 行使用 abs() 函数出错.我选择的编译器:c++(4.3.2)

Getting error with abs() function at line 35 in this code. Compiler I choosed : c++(4.3.2)

看底部的错误.

void bfs(pair<int,int> pixelpos){
bfsq.push(pixelpos);
int u,v,i,j;
pair<int,int> tmpq;
while(!bfsq.empty()){
    tmpq = bfsq.front();
    u = tmpq.first; v = tmpq.second;
    bfsq.pop();
    r(i,u-square_dist,u+square_dist) r(j,v-square_dist,v+square_dist)
      if(inrange(i,j)){
      // ERROR HERE DOWN IN abs() fn
        int dist = abs(pixelpos.first - i) + abs(pixelpos.second -j); // Line: 35
        if(graph[i][j]>dist){
            graph[i][j] = dist;
            bfsq.push(pair<int,int> (i,j));
          }
      }
}

prog.cpp:在函数void bfs(std::pair)"中:

prog.cpp: In function 'void bfs(std::pair)':

prog.cpp:35:错误:重载abs(int)"的调用不明确

/usr/include/c++/4.3/cmath:99:注意:候选对象是:double std::abs(double)/usr/include/c++/4.3/cmath:103: 注意:float std::abs(float)

/usr/include/c++/4.3/cmath:99: note: candidates are: double std::abs(double) /usr/include/c++/4.3/cmath:103: note: float std::abs(float)

/usr/include/c++/4.3/cmath:107: 注意:long double std::abs(long double)

/usr/include/c++/4.3/cmath:107: note: long double std::abs(long double)

prog.cpp:35:错误:重载abs(int)"的调用不明确

/usr/include/c++/4.3/cmath:99: 注意:候选对象是:double std::abs(double)

/usr/include/c++/4.3/cmath:99: note: candidates are: double std::abs(double)

/usr/include/c++/4.3/cmath:103: 注意:float std::abs(float)

/usr/include/c++/4.3/cmath:103: note: float std::abs(float)

/usr/include/c++/4.3/cmath:107: 注意:long double std::abs(long double)

/usr/include/c++/4.3/cmath:107: note: long double std::abs(long double)

可能是什么原因?

推荐答案

错误的原因可能是你没有包含头文件.

The reason for the error can be that you did not include header <cstdlib>.

#include <cstdlib>

标准 C 函数

int abs(int j);

在C头文件中声明.

尽管 C++ 标准允许将标准 C 名称放在全局命名空间中，但最好使用限定名称，例如

Though the C++ Standard allows to place standard C names in the global namespace nevertheless it is better to use qualified names as for example

int dist = std::abs(pixelpos.first - i) + std::abs(pixelpos.second -j);

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