按照该教程 https://aquamentus.com/flex_bison.html 学习flex和bison时，遇到了如下问题

/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libfl.so: undefined reference to `yylex'
collect2: error: ld returned 1 exit status
flex文件：
 
  #include <cstdio>
  #include "snazzle.tab.h"  // to get the token types from Bison
  //extern int yylex();
[ \t\n]           ;
[0-9]+\.[0-9]+    { yylval.fval = atof(yytext); return FLOAT; }
[0-9]+            { yylval.ival = atoi(yytext); return INT; }
[a-zA-Z0-9]+      {
  // We have to strdup yytext because Flex will change it for the next token.
  // Note that this memory must be freed somewhere, so that's why we call
  // free() above in the Bison section.  (Aside: we use free() instead of
  // delete because strdup is a C function that uses malloc, not a C++
  // function that uses new.)
  yylval.sval = strdup(yytext);
  return STRING;
bison文件：
 
  #include <cstdio>
  #include <iostream>
  using namespace std;
  // Declare stuff from Flex that Bison needs to know about:
  extern int yylex();
  extern int yyparse();
  extern FILE *yyin;
  void yyerror(const char *s);
// Bison fundamentally works by asking flex to get the next token, which it
// returns as an object of type "yystype".  Initially (by default), yystype
// is merely a typedef of "int", but for non-trivial projects, tokens could
// be of any arbitrary data type.  So, to deal with that, the idea is to
// override yystype's default typedef to be a C union instead.  Unions can
// hold all of the types of tokens that Flex could return, and this this means
// we can return ints or floats or strings cleanly.  Bison implements this
// mechanism with the %union directive:
%union {
  int ival;
  float fval;
  char *sval;
// Define the "terminal symbol" token types I'm going to use (in CAPS
// by convention), and associate each with a field of the %union:
%token <ival> INT
%token <fval> FLOAT
%token <sval> STRING
// This is the actual grammar that bison will parse, but for right now it's just
// something silly to echo to the screen what bison gets from flex.  We'll
// make a real one shortly:
snazzle:
  INT snazzle      {
      cout << "bison found an int: " << $1 << endl;
  | FLOAT snazzle  {
      cout << "bison found a float: " << $1 << endl;
  | STRING snazzle {
      cout << "bison found a string: " << $1 << endl; free($1);
  | INT            {
      cout << "bison found an int: " << $1 << endl;
  | FLOAT          {
      cout << "bison found a float: " << $1 << endl;
  | STRING         {
      cout << "bison found a string: " << $1 << endl; free($1);
int main(int, char**) {
  // Open a file handle to a particular file:
  FILE *myfile = fopen("a.snazzle.file", "r");
  // Make sure it is valid:
  if (!myfile) {
    cout << "I can't open a.snazzle.file!" << endl;
    return -1;
  // Set Flex to read from it instead of defaulting to STDIN:
  yyin = myfile;
  // Parse through the input:
  yyparse();
void yyerror(const char *s) {
  cout << "EEK, parse error!  Message: " << s << endl;
  // might as well halt now:
  exit(-1);
运行指令：
 
在flex文件中添加%option noyywrap，加入该语句之后，g++指令就不需要添加-lfl参数
 
（-lfl 是为了将flex库文件链接！）
 
修改后的flex文件如下：
 
  #include <cstdio>
  #include "snazzle.tab.h"  // to get the token types from Bison
  //extern int yylex();
%option noyywrap
[ \t\n]           ;
[0-9]+\.[0-9]+    { yylval.fval = atof(yytext); return FLOAT; }
[0-9]+            { yylval.ival = atoi(yytext); return INT; }
[a-zA-Z0-9]+      {
  // We have to strdup yytext because Flex will change it for the next token.
  // Note that this memory must be freed somewhere, so that's why we call
  // free() above in the Bison section.  (Aside: we use free() instead of
  // delete because strdup is a C function that uses malloc, not a C++
  // function that uses new.)
  yylval.sval = strdup(yytext);
  return STRING;
修改后的运行指令如下：
 
                    按照该教程https://aquamentus.com/flex_bison.html学习flex和bison时，遇到了如下问题/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/libfl.so: undefined reference to `yylex'collect2: error: ld returned 1 exit statusflex文件：%{  #include &lt;cstd
				
ubuntu18.04 , cuda10.0 编译darknet出现/usr/bin/ld: cannot find -lcuda
cannot find -lcuda 意思是编译时未找到libcuda库。
首先查看Makefile这中cuda路径是否正确，即下面第四行lib路径
ifeq ($(GPU), 1)
COMMON+= -DGPU -I/usr/local/cuda-10.0/include/
CFLAGS+= -DGPU
LDFLAGS+= -L/usr/local/cuda-10.0/lib64 -lcuda -lcudart -lcublas -lcurand
endif
 /usr/bin/ld: /tmp/ccV9xYuG.o: undefined reference to symbol '_ZN2cv6imreadERKSsi'
/opt/opencv-4.4.0-build/lib64/libopencv_imgcodecs.so.4.4: error adding symbols: DSO missing from command line
collect2: error: ld returned
				
<br />最近在Linux下编程发现一个诡异的现象，就是在链接一个静态库的时候总是报错，类似下面这样的错误：
(.text+0x13): undefined reference to `func' <br />    关于undefined reference这样的问题，网上也有很多的说法，在此，我以详细地示例给出其中的各种原因说明以及解决方法，然后再给出我所遇到的与大家均不同的问题。<br />1.  链接时缺失了相关目标文件（.o）<br />    测试代码如下：<br />
gcc -o main main.c
编译错误提示：
/usr/bin/ld: /tmp/cckwgwIa.o: undefined reference to symbol 'sin@@GLIBC_2.2.5'
/lib/x86_64-linux-gnu/libm.so.6: error adding symbols: DSO mis
/usr/bin/ld: ../../../lib/libcnstream_va.so.6.1.0: undefined reference to `RGB24ToNV12'
/usr/bin/ld: ../../../lib/libcnstream_va.so.6.1.0: undefined reference to `RAWToNV12'
/usr/bin/ld: ../../../lib/libcnstream_va.so.6.1.0: un.
target — 目标文件， 可以是Object File 也可以是可执行文件，还可也是标签Label（标签内容在“伪目标”章节）；
prerequisites—生成target所需的文件或目标；
				
具体报错信息如下：
/usr/bin/ld: /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../lib/Scrt1.o: in function `_start':
(.text+0x24): undefined reference to `main'
一开始看了很多博客都说是main函数写错了，但我的main函数是没写错的。
后来发现可能自己的makefile写的不对，需要让带有main函数的文件在makefile中第一个出现。
					
解决/usr/bin/ld: ../common/common.o: undefined reference to symbol ‘UI_new@@OPENSSL_1.0.0‘//lib/x86_6
				
R源码编译安装前言安装包下载依赖包下载安装编译R总结
一般尽可能的使用编译好的R，或者使用miniconda安装R。 但是使用conda安装一些R包时会遇到各种各样的错误，同时如果需要使用更高版本的R，源码编译则是最好选择。安装过程中不断出现的报错让人头疼，这里简要记录安装遇到的报错及解决，有参考网上其他教程，一并谢过。 常见过程一笔带过。
安装包下载
环境：CentOS release 6...
当前工程的需求是把调用了boost库的C++工程编译成为一个动态链接库以供Python调用，（boos
的使用过程也有些曲折，详细过程及模板伪代码请见本人的这篇博客： ），但是在调整完成wrapper.cc后，编译，报错提示
/usr/bin/ld: ../lib/libXXX.a(XXX.cc.o): relocation R_X86_64_PC32 against symbol `_ZN8planning4eudm31_LonSim