1、memset是計算機中C/C++語言函數(shù)。將s所指向的某一塊內(nèi)存中的前n個 字節(jié)的內(nèi)容全部設(shè)置為ch指定的ASCII值， 第二個值為指定的內(nèi)存地址，塊的大小由第三個參數(shù)指定，這個函數(shù)通常為新申請的內(nèi)存做初始化工作， 其返回值為指向s的指針。
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函數(shù)介紹：void *memset(void *s, int ch, size_t n);
2、函數(shù)解釋：將s中前n個字節(jié) （typedef unsigned int size_t ）用 ch 替換并返回 s 。
memset：作用是在一段內(nèi)存塊中填充某個給定的值，它是對較大的結(jié)構(gòu)體或數(shù)組進行清零操作的一種最快方法。
3、范例：
在go語言中使用viper之類的庫很方便的處理yaml配置文件，但是在c語言中就比較麻煩，經(jīng)過一番思索和借助強大的github,發(fā)現(xiàn)了一個libyaml c庫，但是網(wǎng)上的例子都比較麻煩，而且比較繁瑣，就想法作了一個相對比較容易配置的解析應用，可以簡單地類似viper 的模式進行配置實現(xiàn)不同的配置文件讀取。如你的配置文件很復雜請按格式修改KeyValue 全局變量，歡迎大家一起完善
庫請自行下載 GitHub - yaml/libyaml: Canonical source repository for LibYAML
直接上代碼
yaml示例文件
%YAML 1.1
---
mqtt:
subtopic: "Control/#"
pubtopic: "bbt"
qos: 1
serveraddress: "tcp://192.168.0.25:1883"
clientid: "kvm_test"
writelog: false
writetodisk: false
outputfile: "./receivedMessages.txt"
hearttime: 30
#ifndef __CONFIG_H__
#define __CONFIG_H__
#ifdef __cplusplus
extern "C" {
#endif
/************************/
/* Minimum YAML version */
/************************/
#define YAML_VERSION_MAJOR 1
#define YAML_VERSION_MINOR 1
#define STRUCT_TYPE_NAME 100
#define INT_TYPE_NAME 101
#define STRING_TYPE_NAME 102
#define BOOL_TYPE_NAME 103
#define FLOAT_TYPE_NAME 104
#define MAP_TYPE_NAME 105
#define LIST_TYPE_NAME 106
typedef struct{
char *key;
void *value;
int valuetype;
char *parent;
}KeyValue,*pKeyValue;
#ifdef __cplusplus
}
#endif
#endif
#include
#include
#include
#include
#include
#include
#include
#include "config.h"
typedef struct {
char *SUBTOPIC; //string `yaml:"subtopic" mapstructure:"subtopic"` //"topic1"
char *PUBTOPIC; //string `yaml:"pubtopic" mapstructure:"pubtopic"`
int QOS; //byte `yaml:"qos" mapstructure:"qos"` //1
char *SERVERADDRESS; //string `yaml:"serveraddress" mapstructure:"serveraddress"` //= "tcp://mosquitto:1883"
char *CLIENTID; //string `yaml:"clientid" mapstructure:"clientid"` //= "mqtt_subscriber"
int HEARTTIME; //int `yaml:"hearttime" mapstructure:"hearttime"`
// CommandLocalPath string `yam:"commanlocalpath"`
}mqttSection,*pmqttSection;
typedef struct {
mqttSection Mqtt;// `yaml:"mqtt" mapstructure:"mqtt"`
// KVM kvmSection `yaml:"kvm" mapstructure:"kvm"`
}ConfigT;
ConfigT config;
static KeyValue webrtcconfig[]={
{"mqtt",config,STRUCT_TYPE_NAME,NULL},
{"subtopic",(config.Mqtt.SUBTOPIC),STRING_TYPE_NAME,"mqtt"},
{"pubtopic",(config.Mqtt.PUBTOPIC),STRING_TYPE_NAME,"mqtt"},
{"qos",(config.Mqtt.QOS),INT_TYPE_NAME,"mqtt"},
{"serveraddress",(config.Mqtt.SERVERADDRESS),STRING_TYPE_NAME,"mqtt"},
{"clientid",(config.Mqtt.CLIENTID),STRING_TYPE_NAME,"mqtt"},
{"hearttime",(config.Mqtt.HEARTTIME),INT_TYPE_NAME,"mqtt"},
{NULL,NULL,0,NULL},
};
int printConfig(ConfigT * pconfig){
if(pconfig==NULL) return -1;
printf("mqtt:r ");
if(pconfig-Mqtt.SUBTOPIC!=NULL) {printf("subtopic: %sr ",pconfig-Mqtt.SUBTOPIC); }
if(pconfig-Mqtt.SUBTOPIC!=NULL) {printf("pubtopic: %sr ",pconfig-Mqtt.PUBTOPIC); }
printf("qos: %dr ",config.Mqtt.QOS);
if(pconfig-Mqtt.SERVERADDRESS!=NULL) {printf("serveraddress: %sr ",pconfig-Mqtt.SERVERADDRESS); }
if(pconfig-Mqtt.CLIENTID!=NULL) {printf("clientid: %sr ",pconfig-Mqtt.CLIENTID); }
printf("hearttime: %dr ",config.Mqtt.HEARTTIME);
}
int freeConfig(ConfigT * pconfig){
if(pconfig==NULL) return -1;
if(pconfig-Mqtt.SERVERADDRESS!=NULL) {free(pconfig-Mqtt.SERVERADDRESS); }
if(pconfig-Mqtt.CLIENTID!=NULL) {free(pconfig-Mqtt.CLIENTID); }
if(pconfig-Mqtt.SUBTOPIC!=NULL) {free(pconfig-Mqtt.SUBTOPIC); }
}
char currentkey[100];
void getvalue(yaml_event_t event,pKeyValue *ppconfigs){
char *value = (char *)event.data.scalar.value;
pKeyValue pconfig=*ppconfigs;
char *pstringname;
while(pconfig-key!=NULL){
if(currentkey[0]!=0){
if(!strcmp(currentkey,pconfig-key))
{
switch(pconfig-valuetype){
case STRING_TYPE_NAME:
pstringname=strdup(value);
printf("get string value %sr ",pstringname);
*((char**)pconfig-value)=pstringname;
memset(currentkey, 0, sizeof(currentkey));
break;
case INT_TYPE_NAME:
*((int*)(pconfig-value))=atoi(value);
memset(currentkey, 0, sizeof(currentkey));
break;
case BOOL_TYPE_NAME:
if(!strcmp(value,"true")) *((bool*)(pconfig-value))=true;
else *((bool*)(pconfig-value))=false;
memset(currentkey, 0, sizeof(currentkey));
break;
case FLOAT_TYPE_NAME:
*((float*)(pconfig-value))=atof(value);
memset(currentkey, 0, sizeof(currentkey));
break;
case STRUCT_TYPE_NAME:
case MAP_TYPE_NAME:
case LIST_TYPE_NAME:
memset(currentkey, 0, sizeof(currentkey));
strncpy(currentkey,value,strlen(value));
break;
default:
break;
}
break;
}
//continue;
}else{
if(!strcmp(value,pconfig-key)){
strncpy(currentkey,pconfig-key,strlen(pconfig-key));
break;
}
}
pconfig++;
}
}
int Load_YAML_Config( char *yaml_file, KeyValue *(configs[]) )
{
struct stat filecheck;
yaml_parser_t parser;
yaml_event_t event;
bool done = 0;
unsigned char type = 0;
unsigned char sub_type = 0;
if (stat(yaml_file, filecheck) != false )
{
printf("[%s, line %d] Cannot open configuration file '%s'! %s", __FILE__, __LINE__, yaml_file, strerror(errno) );
return -1;
}
FILE *fh = fopen(yaml_file, "r");
if (!yaml_parser_initialize(parser))
{
printf("[%s, line %d] Failed to initialize the libyaml parser. Abort!", __FILE__, __LINE__);
return -1;
}
if (fh == NULL)
{
printf("[%s, line %d] Failed to open the configuration file '%s' Abort!", __FILE__, __LINE__, yaml_file);
return -1;
}
memset(currentkey, 0, sizeof(currentkey));
/* Set input file */
yaml_parser_set_input_file(parser, fh);
while(!done)
{
if (!yaml_parser_parse(parser, event))
{
/* Useful YAML vars: parser.context_mark.line+1, parser.context_mark.column+1, parser.problem, parser.problem_mark.line+1, parser.problem_mark.column+1 */
printf( "[%s, line %d] libyam parse error at line %ld in '%s'", __FILE__, __LINE__, parser.problem_mark.line+1, yaml_file);
}
if ( event.type == YAML_DOCUMENT_START_EVENT )
{
//yaml file first line is version
//%YAML 1.1
//---
yaml_version_directive_t *ver = event.data.document_start.version_directive;
if ( ver == NULL )
{
printf( "[%s, line %d] Invalid configuration file. Configuration must start with "%%YAML 1.1"", __FILE__, __LINE__);
}
int major = ver-major;
int minor = ver-minor;
if (! (major == YAML_VERSION_MAJOR minor == YAML_VERSION_MINOR) )
{
printf( "[%s, line %d] Configuration has a invalid YAML version. Must be 1.1 or above", __FILE__, __LINE__);
return -1;
}
}
else if ( event.type == YAML_STREAM_END_EVENT )
{
done = true;
}
else if ( event.type == YAML_MAPPING_END_EVENT )
{
sub_type = 0;
}
else if ( event.type == YAML_SCALAR_EVENT )
{
getvalue(event,configs);
}
}
return 0;
}
int main(int argc, char *argv[]){
pKeyValue pconfig=webrtcconfig[0];
Load_YAML_Config("../../etc/kvmagent.yml",pconfig);
printConfig(config);
freeConfig(config);
}
在你申請了一塊內(nèi)存之后，
比如
int*p=null;
p=malloc(10*sizeof(int));//申請了10個int型內(nèi)存
memset(p,0,10*sizeof(int));//全部初始化為0
memset的作用就是把你快連續(xù)的內(nèi)存初始化為你給的值。
example
/*memset.c:thisprogramusesmemsetto
*setthefirstfourbytesofbufferto"*".
*/
#includememory.h
#includestdio.h
voidmain(void)
{
charbuffer[]="thisisatestofthememsetfunction";
printf("before:%s\n",buffer);
memset(buffer,'*',4);
printf("after:%s\n",buffer);
}
output
before:thisisatestofthememsetfunction
after:****isatestofthememsetfunction
memset是個函數(shù)，百它在string.h頭文件中有聲明。它有三個參數(shù)，一度是所要set的首地址，二是set的值問，三是set的字節(jié)數(shù)。
string.h在c語言和c++語言中都被廣泛的使用，但是具體情況不是很一樣。由于傳統(tǒng)的C++脫胎于C，所以傳統(tǒng)C++中于C語言中對本詞條的用法差不多，經(jīng)過美國標準化組織修改標準化后的標準C++中，定義則是大不相同。
擴展資料：
程序例：
#includestdio.h?#includestring.h?int?main(void)?{?char?string[10];?char*str1="abcdefghi";?strcpy(string,str1);?printf("%s\n",string);?return?0;?}
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