linux下c/c++日志记录及文件读取

1、日志记录

（1）代码writelog.cpp

 /*日志记录*/
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
 #include <unistd.h>
 #include <assert.h>
 #include <string.h>
 #include <string>
 #include <fcntl.h>
 #include <stdarg.h>

 enum switch_mode
 {
     mode_minute,
     mode_hour,
     mode_day,
     mode_month
 };
 int file_fd = -1;
 int log_file(switch_mode mode = mode_day)
 {
     char file_path[512] = {0};
     char filetime[32] = {0};
     struct tm tm_time;
     time_t t_log;
     std::string log_time = "";

     assert(getcwd(file_path, 512) != NULL);    //当前目录
     if (file_path[strlen(file_path) - 1] != '/') {
         file_path[strlen(file_path)] = '/';
     }
     if(access(file_path, F_OK) != 0) {     //目录不存在
         std::string build_path ="mkdir -p ";
         build_path += file_path;
         assert(system(build_path.c_str()) !=0 );
     }

     t_log = time(NULL);
     localtime_r(&t_log, &tm_time);
     strftime(filetime, sizeof(filetime), "%Y%m%d%H%M%S", &tm_time); //日志的时间
     switch(mode) {  //日志存储模式
     case mode_minute:
         log_time.assign(filetime, 0, 12);
         break;
     case mode_hour:
         log_time.assign(filetime, 0, 10);
         break;
     case mode_day:
         log_time.assign(filetime, 0, 8);
         break;
     case mode_month:
         log_time.assign(filetime, 0, 6);
         break;
     default:
         log_time.assign(filetime, 0, 8);
     }
     strcat(file_path, "log_");
     strcat(file_path, log_time.c_str());
     strcat(file_path, ".log");

     file_fd = open(file_path, O_RDWR|O_CREAT|O_APPEND, 0666);
     assert(file_fd != -1);
     return 0;
 }
 void write_cmd(const char *fmt,...)
 {
     va_list ap;
     va_start(ap,fmt);
     vprintf(fmt,ap);
     va_end(ap);
 }
 int write_log(const char *msg, ...)
 {
     char final[2048] = {0};   //当前时间记录
     va_list vl_list;
     va_start(vl_list, msg);
     char content[1024] = {0};
     vsprintf(content, msg, vl_list);   //格式化处理msg到字符串
     va_end(vl_list);

     time_t  time_write;
     struct tm tm_Log;
     time_write = time(NULL);        //日志存储时间
     localtime_r(&time_write, &tm_Log);
     strftime(final, sizeof(final), "[%Y-%m-%d %H:%M:%S] ", &tm_Log);

     strncat(final, content, strlen(content));
     assert(msg != NULL && file_fd != -1);
     assert( write(file_fd, final, strlen(final)) == strlen(final));
     return 0;
 }
 void close_file()
 {
     close(file_fd);
 }
 /******************日志记录测试******************/
 int main()
 {
     log_file();
     write_cmd("the address for cmd:%d\n", 100);
     write_log("the address for log:%d\n", 200);
     close_file();
     return 0;
 }

（2）编译运行

 g++ -o writelog writelog.cpp

运行控制台显示：

文件log_20151105.log内容：

2、文件读取

（1）代码readdata.c

 #include <stdio.h>
 #include <stdlib.h>
 #include <assert.h>
 int read_file(char *file_name)
 {
     char *buff;
     FILE *fp = fopen(file_name, "r+");
     assert(fp);
     int flag = fseek(fp, 0, SEEK_END);
     assert(flag == 0);
     int len = ftell(fp);
     buff = (char *)malloc(sizeof(char) * (len + 1));
     flag = fseek(fp, 0, SEEK_SET);
     assert(flag == 0);

     int num = fread(buff, 1, len + 1, fp);
     assert(num == len);

     printf("len:%d, num:%d, buff:%s", len, num, buff);
     free(buff);
     buff = NULL;
     fclose(fp);
     return 0;
 }
 int read_file_p(char *file_name)
 {
     char buff[1024] = {0};
     FILE *fp = fopen(file_name, "r+");
     assert(fp);
     int ch;
     int i = 0;
     do {
         ch = fgetc(fp);
         buff[i++] = ch;
     } while(ch != EOF);
     buff[i - 2] = '\0';
     fclose(fp);

     printf("buff:%s\n", buff);
     return 0;
 }
 int main(int argc, char *argv[])
 {
     assert(argc == 2);
     read_file(argv[1]);
     read_file_p(argv[1]);
     return 0;
 }

（2）编译运行

 gcc -o readdata readdata.c
 ./readdata log_20151105.log