使用getchar()出现'initializer element is not constant'错误的咨询

原代码 #

#include <stdio.h>
#include <stdbool.h>

typedef enum{
  counting1,
  counting2,
  searching,
  possiblecom,
  possibleend,
} read_state;

bool issep(char a){
  return (a == ' ' || a == '\n' || a == '\t');
}

read_state state = searching;
int count = 0;
int c = getchar(); // 错误点1：全局变量用函数调用初始化

bool wasword = false;

// 错误点2：while循环直接放在全局作用域，不是函数内
while (c != -1)
{
  if(state == searching)
  {
    if(c == '{'){state = counting1;}
    else if(c == '('){state = possiblecom;}
  }else
  {
    if(state == counting2 && c == '*'){
      c = getchar();
      if(c == ')'){
        state = searching;
        if(wasword = true){
          count++;
        }
      }else{
        if (issep(c)){
          if (wasword == true){count++;}
          wasword = false;
        }else{wasword = true;}
      }
    }
    
    else if(state = counting1 && c == '}'){state = searching;}
    
    else if (state == counting1 || state == counting2){
      if (issep(c) == false){
        wasword = true;
      }
      else{
        if(wasword == true){count++;}
        wasword = false;
      }
    }
  }
  
  c = getchar();
  
  if(state = possiblecom){
    if(c == '*'){
      state = counting2;
      c = getchar();
      wasword = false;
    }else{state = searching;}
  }
}

// 错误点3：printf直接放在全局作用域，不是函数内
printf("%d", count);

报错信息 #

1: comcount.c:24:9: error: initializer element is not constant
   24 | int c = getchar();
      |         ^~~~~~~
2: comcount.c:28:1: error: expected identifier or ‘(’ before ‘while’
   28 | while (c != -1)
      | ^~~~~
3:comcount.c:84:8: error: expected declaration specifiers or ‘...’ before string constant
   84 | printf("%d", count);
      |        ^~~~
  comcount.c:84:14: error: expected declaration specifiers or ‘...’ before ‘count’
   84 | printf("%d", count);
      |              ^~~~~

错误原因分析 #

1. 全局变量初始化规则限制：全局变量的存储空间在程序启动阶段就分配完成，初始化值必须是编译期就能确定的常量。getchar()是运行时执行的函数调用，返回值只有程序运行时才能确定，因此不能用来初始化全局变量c。你之前能正常运行int c = getchar();，是因为那段代码写在函数内部（比如main函数里），局部变量允许使用运行时表达式初始化。

2. 代码逻辑不能直接置于全局作用域：C语言规定，函数外部的全局作用域只能存放变量声明、函数声明或预处理指令，不能直接编写while循环、printf这类执行语句。你的while循环和printf直接放在全局作用域，编译器会将其当作声明解析，因此报错。

修复方案 #

将所有执行逻辑（while循环、getchar调用、printf）放入main函数内部，全局变量可保留声明（也可改为局部变量）。修复后的代码如下：

#include <stdio.h>
#include <stdbool.h>

typedef enum{
  counting1,
  counting2,
  searching,
  possiblecom,
  possibleend,
} read_state;

bool issep(char a){
  return (a == ' ' || a == '\n' || a == '\t');
}

int main() {
    read_state state = searching;
    int count = 0;
    int c = getchar(); // 局部变量可使用getchar()初始化
    bool wasword = false;

    while (c != -1)
    {
      if(state == searching)
      {
        if(c == '{'){state = counting1;}
        else if(c == '('){state = possiblecom;}
      }else
      {
        if(state == counting2 && c == '*'){
          c = getchar();
          if(c == ')'){
            state = searching;
            if(wasword){ // 简化判断，替换原错误的赋值操作
              count++;
            }
          }else{
            if (issep(c)){
              if (wasword){count++;}
              wasword = false;
            }else{wasword = true;}
          }
        }
        
        else if(state == counting1 && c == '}'){state = searching;} // 修正为相等判断，替换原赋值操作
        
        else if (state == counting1 || state == counting2){
          if (!issep(c)){
            wasword = true;
          }
          else{
            if(wasword){count++;}
            wasword = false;
          }
        }
      }
      
      c = getchar();
      
      if(state == possiblecom){ // 修正为相等判断，替换原赋值操作
        if(c == '*'){
          state = counting2;
          c = getchar();
          wasword = false;
        }else{state = searching;}
      }
    }

    printf("%d", count);
    return 0;
}

额外注意：原代码存在多处逻辑错误，把判断相等的==写成了赋值操作=（比如else if(state = counting1 && c == '}')），这些会导致程序逻辑偏离预期，已在修复代码中修正。

内容的提问来源于stack exchange，提问作者OctoPussy