#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* argv[])
{
char ch
FILE* fp
unsigned long int count = 0
char buf[1025] = {0}
// 这里要求我们在输入两个参数，第一个为 exe 路径，第二个为 文件名
// 如 file_test.exe test.txt
if (argc != 2)
{
printf("Usage: %s filename\n", argv[0])
exit(EXIT_FAILURE)
}
if ((fp = fopen(argv[1], "r")) == NULL)
{
// 如果文件打开失败（通常是文件不存在），则结束程序
printf("Can't open %s\n", argv[1])
exit(EXIT_FAILURE)
}
while ((ch = getc(fp)) != EOF &&count <1024)
{
// 显示文本内容并计数
buf[count] = ch
count++
}
fclose(fp)
printf("%s\n", buf)
printf("File %s has %lu characters\n", argv[1], count)
return 0
}
2、cJSON解析字符串
编译选项要加 -lm
示例源串
{
"server": {
"nodes": [{
"ip": "10.76.76.190",
"port": 6379
}, {
"ip": "10.76.76.191",
"port": 6380
}, {
"ip": "10.76.76.192",
"port": 6381
}],
"password": "admin"
},
"isssl": true
}
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示例代码（每一行记得判空，编译时加-lm选项）
#include <stdio.h>
#include "cJSON.h"
int main(){
char c[] = "{\"server\":{\"nodes\":[{\"ip\":\"10.76.76.190\",\"port\":6379},{\"ip\":\"10.76.76.191\",\"port\":6380},{\"ip\":\"10.76.76.192\",\"port\":6381}],\"password\":\"admin\"},\"isssl\":true}"
cJSON* root = cJSON_Parse(c)
cJSON* json_server = cJSON_GetObjectItem(root, "server")
cJSON* json_isssl = cJSON_GetObjectItem(root, "isssl")
cJSON* json_password = cJSON_GetObjectItem(json_server, "password")
cJSON* json_nodes = cJSON_GetObjectItem(json_server, "nodes")
int i = 0
for (i != cJSON_GetArraySize(json_nodes)++i) {
cJSON* each = cJSON_GetArrayItem(json_nodes, i)
cJSON* json_ip = cJSON_GetObjectItem(each, "ip")
cJSON* json_port = cJSON_GetObjectItem(each, "port")
printf("ip %s\n", json_ip->valuestring)
printf("port %d\n", json_port->valueint)
}
printf("password %s\n", json_password->valuestring)
printf("is ssl %s\n", json_isssl->valueint ? "true":"false")
cJSON_Delete(root)
}
3、curl拿到回传的数据
编译选项要加 -lcurl
头部选项参考
https://curl.se/libcurl/c/curl_easy_setopt.html
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl/curl.h>
struct string {
char* ptr
size_t len
}
void init_string(struct string* s) {
s->len = 0
s->ptr = malloc(s->len + 1)
if (s->ptr == NULL) {
fprintf(stderr, "malloc() failed\n")
exit(EXIT_FAILURE)
}
s->ptr[0] = '\0'
}
size_t writefunc(void* ptr, size_t size, size_t nmemb, struct string* s) {
size_t new_len = s->len + size * nmemb
s->ptr = realloc(s->ptr, new_len + 1)
if (s->ptr == NULL) {
fprintf(stderr, "realloc() failed\n")
exit(EXIT_FAILURE)
}
memcpy(s->ptr + s->len, ptr, size * nmemb)
s->ptr[new_len] = '\0'
s->len = new_len
return size * nmemb
}
int main(void) {
CURL* curl
CURLcode res
curl = curl_easy_init()
if(curl) {
struct string s
init_string(&s)
curl_easy_setopt(curl, CURLOPT_URL, "https://www.baidu.com")
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "test")
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writefunc)
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &s)
res = curl_easy_perform(curl)
printf("打印数据:\n%s", s.ptr)
free(s.ptr)
/* always cleanup */
curl_easy_cleanup(curl)
}
return 0
}
4、获取随机数
#include <stdio.h>
int main(int argc, char* argv[]){
srand((int)time(0))
//打印 32位 test 随机数，并用16进制表示
int test2 = rand()
printf("%lx \n", test2)
// 打印 64位 test 随机数，并用16进制表示， 016代表不足16位的部分，补零，llx代表打印64位的16进制数
unsigned long long test = ((unsigned long long)rand() <<32) + rand()
printf("%016llx \n", test)
return 0
}
5、定义按位的结构体
总结，按照位定义结构体，一定要都按照位定义，不然会出现意想不到的错误，而且一定要定义无符号的
#include <stdio.h>
#pragma pack (1)
struct test1 {
unsigned char cloud_id:3
unsigned char vendor_id:4
unsigned short machine_id
unsigned long long current_time:41
}
struct test2 {
unsigned char cloud_id:3
unsigned char vendor_id:4
unsigned short machine_id:16
unsigned long long current_time:41
}
int main(int argc, char* argv[]){
printf("test1 大小 : %d \n", sizeof(struct test1))
printf("test2 大小 : %d \n", sizeof(struct test2))
return 0
}
6、按位打印01字节码
#include <stdio.h>
// 修改type后面的类型，可以查看各种数的字节码
#define type unsigned int
void print_bin(type num)
{
int len = sizeof(type)
int n = 8
int i, j, k
unsigned char *p = (unsigned char*)&num + len -1
for (i = 0i <leni++) //处理len个字节
{
j = *(p - i)//取每个字节的首地址
for ( k = 7k >= 0k--) //处理每个字节的8个位
{
if (j &(1 <<k))
printf("1")
else
printf("0")
}
printf(" ")
}
printf("\r\n")
}
int main(int argc, char* argv[]){
type a = 100
print_bin(a)
return 0
}
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7、打印16进制字节码
#include<stdio.h>
typedef unsigned char uint8
#define HEXDUMP_LINE_LENGTH 16
void hex_dump(uint8* data, int length)
{
uint8* p = data
int i, line, offset = 0
while (offset <length)
{
printf("%04x ", offset)
line = length - offset
if (line >HEXDUMP_LINE_LENGTH)
line = HEXDUMP_LINE_LENGTH
for (i = 0i <linei++)
printf("%02x ", p[i])
for (i <HEXDUMP_LINE_LENGTHi++)
printf(" ")
for (i = 0i <linei++)
printf("%c", (p[i] >= 0x20 &&p[i] <0x7F) ? p[i] : '.')
printf("\n")
offset += line
p += line
}
}
8、打印字节码简易版
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void main() {
unsigned char Buf[] = "123456"
unsigned int len = strlen(Buf)
char* Buf1 = (char*)malloc(len * 3 + 1)
int i = 0, k = 0
for (i <len * 3i += 3, k++)
snprintf(&Buf1[i], 4, "%02x ", Buf[k])
printf(Buf1)
free(Buf1)
}
9、逐级创建文件夹
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
int mkdir_recursively(char* dir) {
if (NULL == dir)
return 1
size_t len = strlen(dir)
char* str = malloc(len + 1)
if (NULL == str)
return 1
strcpy(str, dir)
int i = 0
for (i = 0i <leni++) {
if (str[i] == '/') {
if (i == 0)
continue
str[i] = '\0'
if (access(str, 0) != 0) {
if (mkdir(str, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH)) {
free(str)
return 1
}
}
str[i] = '/'
}
}
if (len >0 &&access(str, 0) != 0) {
if (mkdir(str, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH)) {
free(str)
return 1
}
}
free(str)
return 0
}
int main() {
mkdir_recursively("/home/test/abc/edf")
我现在用的是cJSON这个JSON库，在github上可以下载到，是开源的，Windows和Linux系统开发都可以用。而且是最轻量级的JSON库，下载下来之后再解压，只需要将里面的cJSON.c和cJSON.h这两个文件复制到你的项目（源码）目录就可以了（需要调用cJSON的那个代码文件要加上一句#include "cJSON.h"）。使用起来也超简单，通过阅读cJSON.h中的函数注释和github上面的说明你就会知道怎么用。java实现JSON打包UDP cJSON支持在C程序中创建和解析JSON数据，其提供多种方法供C程序使用，最直接的是将cJSON.c和cJSON.h加入到C工程中
（1） QJsonObject用于在Qt中创建JSON对象
（2）数据传输通过UDP运行
代码如下
首先在pro文件中加入
QT += network
h文件内容：
首先在pro文件中加入
QT += network
h文件内容：
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include<QtNetwork>
namespace Ui {
class MainWindow
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0)
~MainWindow()
QUdpSocket *sender
QByteArray byteArray
private slots:
void on_pushButton_clicked()
private:
Ui::MainWindow *ui
}
#endif // MAINWINDOW_H
cpp文件内容：
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include<QJsonObject>
#include<QJsonDocument>
#include<QDebug>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this)
sender = new QUdpSocket(this)
QJsonObject rectJson
rectJson.insert("Type","Rectangle")
rectJson.insert("height",42)
rectJson.insert("widght",23)
QJsonDocument rectJsonDoc
rectJsonDoc.setObject(rectJson)
byteArray = rectJsonDoc.toJson(QJsonDocument::Compact)
}
MainWindow::~MainWindow()
{
delete ui
}
void MainWindow::on_pushButton_clicked()
{
QHostAddress address
address.setAddress(QString("192.168.230.140"))
sender->writeDatagram(byteArray.data(),byteArray.size(),
address,4444)
}
程序通过端口4444，向IP为192.168.230.140的主机发送JSON数据
C程序如下：
{
int sock_fd
char rcv_buff[512]
struct sockaddr_in client_addr
struct sockaddr_in server_addr
int client_len
int rcv_num = -1
if ((sock_fd = socket(AF_INET, SOCK_DGRAM,0)) <0)
{
perror("socket create error\n")
exit(1)
}
memset(&server_addr,0,sizeof(struct sockaddr_in))
server_addr.sin_family = AF_INET
server_addr.sin_port = htons(4444)
server_addr.sin_addr.s_addr = htonl(INADDR_ANY)
client_len = sizeof(struct sockaddr_in)
if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(struct sockaddr_in)) <0)
{
perror("bind socket error.\n")
exit(1)
}
while (1)
{
/*zero the buff of rvbsm and hvbsm? zhp*/
rcv_num= recvfrom(sock_fd, rcv_buff, sizeof(rcv_buff), 0, (struct sockaddr*)&client_addr, &client_len)
if (rcv_num>0)
{
rcv_buff[rcv_num] = '\0'
printf("rx bsm num = %d\n",rcv_num)
//printf()
printf("%s %u says: %s\n",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port),rcv_buff)
//parse_UDP_data(rcv_num,rcv_buff)
if(rcv_buff != NULL)
{
cJSON* pJson = cJSON_Parse(rcv_buff)
if(pJson == NULL)
{
printf("Json Parse failed.\n")
return 0
}
cJSON* pSub1 = cJSON_GetObjectItem(pJson,"Type")
cJSON* pSub2 = cJSON_GetObjectItem(pJson,"height")
cJSON* pSub3 = cJSON_GetObjectItem(pJson,"widght")
if(pSub1!=NULL)
{
printf("Type : %s\n", pSub1->valuestring)
}
if(pSub2!=NULL)
{
printf("height : %d\n", pSub2->valueint)
}
if(pSub3!=NULL)
{
printf("widght : %d\n", pSub3->valueint)
}
}
}
else
{
perror("recv BSM error\n")
break
}
}
close(sock_fd)
}
编译C程序:gcc -I. -lm -o rencode *.c
由于cJSON使用了标准数学库，所以在编译中需链接其库文件-lm；
在IP为192.168.230.140的Linux服务器中执行./rencode
输出结果为：
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