使用ctypes在Python中映射C结构体时遇类型错误求助

问题重现 #

C代码（c_file.c） #

#include<stdio.h>

struct SomeStructure{
    int age;
    char c;
    char* name;
};

double someFunction(struct SomeStructure *s){
    printf("My age is %d and my c is %s and finally name is %s", s->age, s->c, s->name);
    return 42;
}

编译命令 #

gcc -fPIC -shared -o clibrary.so c_file.c

Python代码（py_file.py） #

import ctypes

clibrary = ctypes.CDLL("./clibrary.so")

class SomeStructure(ctypes.Structure):
    _fields_ = [
        ('age', ctypes.c_int),
        ('c', ctypes.c_char),
        ('name', ctypes.c_char_p)
    ]

clibrary.someFunction.restype = ctypes.c_double
clibrary.someFunction.argtypes = [ctypes.POINTER(SomeStructure)]

obj = SomeStructure(13, 'm', b"Jo")
clibrary.someFunction(ctypes.byref(obj))

错误信息 #

obj = SomeStructure(13, 'm', b"Jo")
TypeError: one character bytes, bytearray or integer expected

解决步骤 #

• 修正char类型的赋值错误
  ctypes.c_char类型要求传入单字节对象（比如b'm'）或者对应的ASCII整数（比如109），不能直接传字符串'm'。修改结构体实例化代码：

  obj = SomeStructure(13, b'm', b"Jo")
  # 或者用ASCII整数：obj = SomeStructure(13, 109, b"Jo")
  

• 修复C代码中的printf格式符错误
  C代码里s->c是char类型，应该用%c格式符，而不是%s（%s用于字符串指针），否则会导致未定义行为（程序崩溃或乱码）。修改后的C函数：

  double someFunction(struct SomeStructure *s){
      printf("My age is %d and my c is %c and finally name is %s", s->age, s->c, s->name);
      return 42;
  }
  

• 重新编译并运行
  重新执行编译命令生成新的共享库，再运行Python代码即可正常输出：

  My age is 13 and my c is m and finally name is Jo
  

内容的提问来源于stack exchange，提问作者Avv