头文件中声明函数的链接器混淆 (C)

Question

所以我在上 C 编程课程，我认为自己是一名优秀的程序员，但我遇到了一些我不太明白如何思考的事情。我正在编写一个使用多个头文件并有两个用于创建可执行文件的 c 文件的压缩器。我已经正确地包含了头文件（我认为），将它们放在同一个目录中并说

#include "myLib.h"

现在。这是我坚持的部分。在一个文件中，我有一个调用头文件中声明的函数的主要方法。这些函数的源代码在我之前提到的另一个 .c 文件中。当我编译时：

gcc -Wall TestCmp.c LZWCmp.o  

其中 TestCmp.c 是包含主文件的文件，LZWCmp.o 是另一个 .c 文件的目标文件。 我收到编译错误，告诉我四个声明的方法中的三个是未定义的引用。为什么链接器会接受其中一种方法存在而其他三种不存在？？？

任何帮助将不胜感激。谢谢！

这是 TestCmp.c 的源代码

#include <stdio.h>
#include <assert.h>
#include <limits.h>
#include "LZWCmp.h"
#include "SmartAlloc.h"
#include "MyLib.h"

/*function pointer to the CodeSink function in TestCmp, which function simply prints  each 4-byte uint sent to it as 8 hex digits. It does so 8 integers per line, with one space between each pair of integers, and no space after the final integer, just an EOL.*/
void sink(void *pointer, uint code) {
    printf("%08X ", code);
}

void main() {
   int numCodes; /*Number of codes that compressor starts with understanding*/
   LZWCmp *cmp = malloc(sizeof(struct LZWCmp)); /*allocate memory for compressor state*/
   CodeSink ptr = sink; /*set sodesink pointer to sink function*/
   uchar letter; /*letter for intake and compression*/

   printf("Enter symbol count: ");
   scanf(" %d", &numCodes);
   while(letter != '\n') {
      letter = getchar();
   }

   LZWCmpInit(cmp, numCodes, ptr, NULL); /*Initialize compressor */

   while(letter < UCHAR_MAX) {
      letter = getchar(); 
      LZWCmpEncode(cmp, letter);     /*Send letter to encoder*/ /*FIRST FUNCTION TO NOT WORK*/
   }

   LZWCmpStop(cmp); /*Finish program when finding EOF character*/
   LZWCmpDestruct(cmp); /*Free memory space*/

}

还有 myLib.h 的源代码

#ifndef MYLIB_H
#define MYLIB_H

#define BITS_PER_BYTE 8

typedef unsigned char uchar;
typedef unsigned long ulong;
typedef unsigned int uint;
typedef unsigned short ushort;

#ifdef LITTLE_ENDIAN

#define UShortEndianXfer(val) ((val) >> 8 | (val) << 8}

#else

#define UShortEndianXfer(val) (val)

#endif

#endif

以及 LZWCmp.h 的来源

#ifndef LZW_H
#define LZW_H

#include "MyLib.h"

#define RECYCLE_CODE 4096  // Recycle dictionary rather than add this code

/* Function pointer to method to call when a code is completed and ready for
 * transmission or whatever.  The void * parameter can point to anything,
 * and gives hidden information to the function so that it can know what
 * file, socket, etc. the code is going to.  The uint is the next 32 bits
 * worth of compressed output. */
typedef void (*CodeSink)(void *, uint code);

/* One node in a trie representing the current dictionary.  Use symbols
 * to traverse the trie until reaching a point where the link for a
 * symbol is null.  Use the code for the prior link, and add a new code in
 * this case.  Each node has as many links and codes as there are symbols */
typedef struct TrieNode {
    ushort *codes;
    struct TrieNode **links;
} TrieNode;

/* Current state of the LZW compressor. */
typedef struct LZWCmp {
   TrieNode *head;   /* Head pointer to first TrieNode */
   CodeSink sink;   /* Code sink to send bits to */
   void *sinkState;  /* Unknown object to send to sink for state */
   int numSyms;      /* Symbol count, also size of TrieNodes */
   int nextCode;     /* Next code to be assigned */
   int numBits;      /* Number of bits per code currently */
   uint nextInt;     /* Partially-assembled next int of output */
   int bitsUsed;     /* Number of valid bits in top portion of nextInt */
   TrieNode *curLoc; /* Current position in trie */
   short lastSym;    /* Most recent symbol encoded */
} LZWCmp;

/* Initialize a LZWCmp given the number of symbols and the CodeSink
 * to which to send completed codes; */
void LZWCmpInit(LZWCmp *cmp, int numSyms, CodeSink sink, void *sinkState);

/* Encode "sym" using LZWCmp. Zero or more calls of the code sink
 * may result */
 void LZWCmpEncode(LZWCmp *cmp, uchar sym);

/* Mark end of encoding (send next code value to code sink) */
void LZWCmpStop(LZWCmp *cmp);

/* Free all storage associated with LZWCmp (not the sinkState, though,
 * which is "owned" by the caller */
void LZWCmpDestruct(LZWCmp *cmp);

#endif

至于我正在编译的对象，它是教授给我们的一个.o文件，其中包含LZWCmp.h文件中给出的四个函数。如果我们的 TestCmp.c 文件正常工作，那么我应该能够毫无问题地访问 LZCmp.o 文件中的函数。

Answer 1

好的.. 只需对您的代码进行少量修改，我就能够（链接和）编译您的代码.. 文件如下：

文件名：TestCmp.c

#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <limits.h>
#include "LZWCmp.h"
//#include "SmartAlloc.h"
#include "MyLib.h"

/*function pointer to the CodeSink function in TestCmp, which function simply prints  each 4-byte uint sent to it as 8 hex digits. It does so 8 integers per line, with one space between each pair of integers, and no space after the final integer, just an EOL.*/
void sink(void *pointer, uint code) {
    printf("%08X ", code);
}

int main(void) 
{
   int numCodes; /*Number of codes that compressor starts with understanding*/
   LZWCmp *cmp = malloc(sizeof(struct LZWCmp)); /*allocate memory for compressor state*/
   CodeSink ptr = sink; /*set sodesink pointer to sink function*/
   uchar letter; /*letter for intake and compression*/

   printf("Enter symbol count: ");
   scanf(" %d", &numCodes);
   while(letter != '\n') {
      letter = getchar();
   }

   LZWCmpInit(cmp, numCodes, ptr, NULL); /*Initialize compressor */

   while(letter < UCHAR_MAX) {
      letter = getchar(); 
      LZWCmpEncode(cmp, letter);     /*Send letter to encoder*/ /*FIRST FUNCTION TO NOT WORK*/
   }

   LZWCmpStop(cmp); /*Finish program when finding EOF character*/
   LZWCmpDestruct(cmp); /*Free memory space*/

    return 0;

}

文件名：MyLib.h

#ifndef MYLIB_H
#define MYLIB_H

#define BITS_PER_BYTE 8

typedef unsigned char uchar;
typedef unsigned long ulong;
typedef unsigned int uint;
typedef unsigned short ushort;

#ifdef LITTLE_ENDIAN

#define UShortEndianXfer(val) ((val) >> 8 | (val) << 8}

#else

#define UShortEndianXfer(val) (val)

#endif

#endif

文件名：LZWCmp.h

#ifndef LZW_H
#define LZW_H
#include <stdio.h>
#include "MyLib.h"

#define RECYCLE_CODE 4096  // Recycle dictionary rather than add this code

/* Function pointer to method to call when a code is completed and ready for
 * transmission or whatever.  The void * parameter can point to anything,
 * and gives hidden information to the function so that it can know what
 * file, socket, etc. the code is going to.  The uint is the next 32 bits
 * worth of compressed output. */
typedef void (*CodeSink)(void *, uint code);

/* One node in a trie representing the current dictionary.  Use symbols
 * to traverse the trie until reaching a point where the link for a
 * symbol is null.  Use the code for the prior link, and add a new code in
 * this case.  Each node has as many links and codes as there are symbols */
typedef struct TrieNode {
    ushort *codes;
    struct TrieNode **links;
} TrieNode;

/* Current state of the LZW compressor. */
typedef struct LZWCmp {
   TrieNode *head;   /* Head pointer to first TrieNode */
   CodeSink sink;   /* Code sink to send bits to */
   void *sinkState;  /* Unknown object to send to sink for state */
   int numSyms;      /* Symbol count, also size of TrieNodes */
   int nextCode;     /* Next code to be assigned */
   int numBits;      /* Number of bits per code currently */
   uint nextInt;     /* Partially-assembled next int of output */
   int bitsUsed;     /* Number of valid bits in top portion of nextInt */
   TrieNode *curLoc; /* Current position in trie */
   short lastSym;    /* Most recent symbol encoded */
} LZWCmp;

/* Initialize a LZWCmp given the number of symbols and the CodeSink
 * to which to send completed codes; */
void LZWCmpInit(LZWCmp *cmp, int numSyms, CodeSink sink, void *sinkState);

/* Encode "sym" using LZWCmp. Zero or more calls of the code sink
 * may result */
 void LZWCmpEncode(LZWCmp *cmp, uchar sym);

/* Mark end of encoding (send next code value to code sink) */
void LZWCmpStop(LZWCmp *cmp);

/* Free all storage associated with LZWCmp (not the sinkState, though,
 * which is "owned" by the caller */
void LZWCmpDestruct(LZWCmp *cmp);

#endif

文件名：LZWCmp.c（这是我介绍的，将传递给 make 命令 - 见下文）

#include "LZWCmp.h"

void LZWCmpInit(LZWCmp *cmp, int numSyms, CodeSink sink, void *sinkState)
{
    printf("LZWCmpInit \n");
}

void LZWCmpEncode(LZWCmp *cmp, uchar sym)
{
    printf("LZWCmpEncode \n");   
}

void LZWCmpStop(LZWCmp *cmp)
{
    printf("LZWCmpStop \n");
}

void LZWCmpDestruct(LZWCmp *cmp)
{
    printf("LZWCmpDestruct \n");    
}

制作命令：

gcc -Wall TestCmp.c LZWCmp.h MyLib.h LZWCmp.c

希望这会有所帮助！