所以我在一个C编程课程中，我认为自己是一个好的程序员，但是我发现了一些我不太了解如何思考的东西。我正在编写一个使用多个头文件的压缩器，并且有两个用于创建可执行文件的c文件。我通过让它们在同一目录中并且说
来正确地包含头文件（我认为）#include "myLib.h"
现在。这是我坚持的部分。在一个文件中，我有一个main方法调用头文件中声明的函数。这些函数的源代码在我前面提到的另一个.c文件中。当我编译：
gcc -Wall TestCmp.c LZWCmp.o
其中TestCmp.c是包含main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有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不是其他三种方法
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*/
}
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
和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
对于我正在编译的对象，它是由教授提供给我们的.o文件，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。
答案 0 :(得分：1)
好了..对你的代码进行了一些修改，我能够（链接和）编译你的代码..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命令的内容 - 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
希望这有帮助！