c语言：读取文件中的指定内容

      项目中要求从wifi的状态文件中提取出rssi字段的值，还有一个前提条件：必须与hwaddr（手机的MAC地址）一一对应。

wifi状态文件sta_info如下：

# cat /proc/wlan0-vap0/sta_info
-- STA info table -- (active: 1)
1: stat_info...
state: 405
AuthAlgrthm: 0
ieee8021x_ctrlport: 0
hwaddr: c06394e1468b
bssrateset: 82848b960c1218243048606c
aid: 1
tx_bytes: 369918
rx_bytes: 62005
tx_pkts: 333
rx_pkts: 901
tx_fail: 0
tx_avarage:    0
rx_avarage:    0
dz_queue_len: 0
rssi: 62 (62 56)
expired_time: 294
sleep: yes
current_tx_rate: MCS7 65
current_rx_rate: MCS4 39
rx_bw: 20M
tx_bw: 20M
hp_level: 0
QoS Enable: 1
APSD bitmap: 0x0
tx_ra_bitmap: 0x000f0000
Chip Vendor: Broadcom
link_time: 4 min 44 sec
ht_cap: 0c181bff00000000000000000000000000000000000000000000
11n MIMO ps: no limit
Is_8K_AMSDU: 1
amsdu_level: 7895
diffAmpduSz: 0xffffffff
aggre mthd: AMPDU
ht beamformee: N
ht beamformer: N
Activate Tx beamforming : N
ipmc_num: 1
mcmac: 01005e0000fb
bSleep: 01
bDrop: 00
FW bDrop: 00
ht_ie: none
wireless mode: BGN

      我写了一个get_wifi_signal_intensity（const char* mac,char *intenstiy）函数，传入mac地址，输出信号强度值intenstiy，从而实现需求。get_wifi_signal_intensity函数实现如下：

#include "stdio.h"
#include "stdlib.h"
#include "ctype.h"

static void get_wifi_signal_intensity(const char* mac,char *intenstiy)
{
char dstmac[32] = {0};
int i = 0;
int found_mac = 0;
int rssi = 0, dBm = 0;
FILE * fp = NULL;
char filename[64] = {0};
char line[128] = {0};

sprintf(filename,"/proc/wlan0-vap0/sta_info");

if ( mac && (fp = fopen(filename, "r")) )
{
sscanf(mac,"%2s-%2s-%2s-%2s-%2s-%2s",dstmac,dstmac+2,dstmac+4,dstmac+6,dstmac+8,dstmac+10);
for(i=0;i<strlen(dstmac);i++)
{
dstmac[i] = tolower(dstmac[i]);
}

while(!feof(fp))
{
if (NULL == fgets (line, sizeof (line), fp))
{
/* Error or EOF */
break;
}

if ( found_mac )
{
if( strstr(line,"rssi:") )
{
sscanf(line, "%*s %d", &rssi);
break;
}
else
{
continue;
}
}
if( strstr(line,"hwaddr:") && strstr(line,dstmac) )
{
found_mac = 1;
}
}

fclose(fp);
}

if (rssi <= 0)
dBm = -100;
else if (rssi >= 100)
dBm = -50;
else
dBm = (rssi / 2) - 100;

sprintf(intenstiy, "%d", dBm);

printf("MAC is %s,dstmac is %s,rssi is %d,intenstiy is %d",mac,dstmac,rssi,intenstiy);
}

运行结果：

调用函数：get_wifi_signal_intensity("C0-63-94-E1-46-8B",intenstiy)
打印结果：MAC is C0-63-94-E1-46-8B,dstmac is c06394e1468b,rssi is 62,intenstiy is -69

函数实现的功能：
    输入一个MAC地址，格式为C0-63-94-E1-46-8B：1）函数中会去掉MAC中‘-’并将字母全转为小写；2）用转换得到的dstmac 逐行匹配文件内容，直到完全匹配上；3）开始往下在文件中查找rssi字段，并读出来；4）将rssi字段解析出来，只需字段中的数字部分；5）将rssi按对应关系转换成wifi信号强度值intenstiy。