字符串处理分割字符串

**strtok**

分解字符串为一组字符串。s为要分解的字符，delim为分隔符字符（如果传入字符串，则传入的字符串中每个字符均为分割符）。首次调用时，s指向要分解的字符串，之后再次调用要把s设成NULL。
**分解字符串为一组字符串。s为要分解的字符串，delim为分隔符字符串。
例如：strtok(“abc,def,ghi”,”,”)，最后可以分割成为abc def ghi.尤其在点分十进制的IP中提取应用较多。
strtok的函数原型为char strtok(char *s, char *delim)，功能为“Parse S into tokens separated by characters in DELIM.If S is NULL, the saved pointer in SAVE_PTR is used as the next starting point. ” 翻译成汉语就是：作用于字符串s，以包含在delim中的字符为分界符，将s切分成一个个子串；如果，s为空值NULL，则函数保存的指针SAVE_PTR在下一次调用中将作为起始位置。*

strtok()用来将字符串分割成一个个片段。参数s指向欲分割的字符串，参数delim则为分割字符串中包含的所有字符。当strtok()在参数s的字符串中发现参数delim中包含的分割字符时,则会将该字符改为\0 字符。在第一次调用时，strtok()必需给予参数s字符串，往后的调用则将参数s设置成NULL。每次调用成功则返回指向被分割出片段的指针。
例子：

#include<string.h>#include<stdio.h>int main(void){    char input[50]="abc,d,asd,asdf,asd,asd,t";    char*p;    /*strtok places a NULL terminator    infront of the token,if found*/    p=strtok(input,",");    if(p)        printf("%s\n",p);    /*Asecond call to strtok using a NULL    as the first parameter returns a pointer    to the character following the token*/    p=strtok(NULL,",");    if(p)        printf("%s\n",p);    return 0;}

输出：

/home/andrew/文档/IMPORTENT_C/cmake-build-debug/IMPORTENT_CabcdProcess finished with exit code 0

C++例子：

#include<iostream>#include<cstring>using namespace std;int main(){    char sentence[]="This is a sentence with 7 tokens";    cout << "The string to be tokenized is:\n" << sentence << "\n\nThe tokens are:\n\n";    char *tokenPtr=strtok(sentence," ");    while(tokenPtr!=NULL)　{        cout<<tokenPtr<<'\n';        tokenPtr=strtok(NULL," ");    }    //cout << "After strtok,sentence=" << tokenPtr<<endl;    return 0;}

strsep()用于分解字符串为一组字符串。

事例：

#include <stdio.h>#include <memory.h>int main(){    int len, nel;    char query[] ="user_command=appleboy&test=1&test2=2";    char *q, *name, *value;    /* Parse into individualassignments */    q = query;    fprintf(stderr, "CGI[query string] : %s\n",query);    len = strlen(query);    nel = 1;    while (strsep(&q, "&"))        nel++;    fprintf(stderr, "CGI[nel string] : %d\n", nel);    for (q = query; q< (query + len);) {        value = name = q;        /* Skip to next assignment */        fprintf(stderr, "CGI[string] :%s\n", q);        fprintf(stderr, "CGI[stringlen] : %d\n", strlen(q));        fprintf(stderr, "CGI[address] :%p\n", q);        for (q += strlen(q); q < (query +len) && !*q; q++);        /* Assign variable */        name = strsep(&value,"=");        fprintf(stderr, "CGI[name ] :%s\n", name);        fprintf(stderr, "CGI[value] :%s\n", value);    }    return 0;}

/home/andrew/文档/IMPORTENT_C/cmake-build-debug/IMPORTENT_CCGI[query string] : user_command=appleboy&test=1&test2=2CGI[nel string] : 4CGI[string] :user_command=appleboyCGI[stringlen] : 21CGI[address] :0x7ffe5cf043b0CGI[name ] :user_commandCGI[value] :appleboyCGI[string] :test=1CGI[stringlen] : 6CGI[address] :0x7ffe5cf043c6CGI[name ] :testCGI[value] :1CGI[string] :test2=2CGI[stringlen] : 7CGI[address] :0x7ffe5cf043cdCGI[name ] :test2CGI[value] :2Process finished with exit code 0

数据处理，函数格式化输出打印之后的数据处理之—–strtod()函数
strtod()函数

#include<stdlib.h>#include<stdio.h>void main(){    char *endptr;    char a[] = "12345.6789";    char b[] = "1234.567qwer";    char c[] = "-232.23e4";    printf( "a=%lf\n", strtod(a,NULL) );    printf( "b=%lf\n", strtod(b,&endptr) );    printf( "endptr=%s\n", endptr );    printf( "c=%lf\n", strtod(c,NULL) );}

输出结果：

/home/andrew/文档/IMPORTENT_C/cmake-build-debug/IMPORTENT_Ca=12345.678900b=1234.567000endptr=qwerc=-2322300.000000Process finished with exit code 0

char buf[512] = ;sscanf("123456 ", "%s", buf);printf("%s\n", buf);结果为：123456　　2. 取指定长度的字符串。如在下例中，取最大长度为4字节的字符串。sscanf("123456 ", "%4s", buf);printf("%s\n", buf);结果为：1234　　3. 取到指定字符为止的字符串。如在下例中，取遇到空格为止字符串。sscanf("123456 abcdedf", "%[^ ]", buf);printf("%s\n", buf);结果为：123456　　4. 取仅包含指定字符集的字符串。如在下例中，取仅包含1到9和小写字母的字符串。sscanf("123456abcdedfBCDEF", "%[1-9a-z]", buf);printf("%s\n", buf);结果为：123456abcdedf　　5. 取到指定字符集为止的字符串。如在下例中，取遇到大写字母为止的字符串。sscanf("123456abcdedfBCDEF", "%[^A-Z]", buf);printf("%s\n", buf);结果为：123456abcdedf　　6、给定一个字符串iios/12DDWDFF@122，获取 / 和 @ 之间的字符串，先将 "iios/"过滤掉，再将非'@'的一串内容送到buf中sscanf("iios/12DDWDFF@122", "%*[^/]/%[^@]", buf);printf("%s\n", buf);结果为：12DDWDFF　　7、给定一个字符串"hello, world"，仅保留"world"。（注意：“，”之后有一空格）sscanf(“hello, world”, "%*s%s", buf);printf("%s\n", buf);结果为：world　　P.S. %*s表示第一个匹配到的%s被过滤掉，即hello被过滤了，　　如果没有空格则结果为NULL。[2]  

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//Compiled with Visual Studio 2015.//================Original File===================*/// crt_sscanf.c  // compile with: /W3  // This program uses sscanf to read data items  // from a string named tokenstring, then displays them.    #include <stdio.h>    int main( void )  {     char  tokenstring[] = "15 12 14...";     char  s[81];     char  c;     int   i;     float fp;       // Input various data from tokenstring:     // max 80 character string:     sscanf( tokenstring, "%80s", s ); // C4996     sscanf( tokenstring, "%c", &c );  // C4996     sscanf( tokenstring, "%d", &i );  // C4996     sscanf( tokenstring, "%f", &fp ); // C4996     // Note: sscanf is deprecated; consider using sscanf_s instead       // Output the data read     printf( "String    = %s\n", s );     printf( "Character = %c\n", c );     printf( "Integer:  = %d\n", i );     printf( "Real:     = %f\n", fp );  } 

输出：

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%[a-z] 表示匹配a到z中任意字符，贪婪性(尽可能多的匹配)%[aB'] 匹配a、B、'中一员，贪婪性%[^a] 匹配非a的任意字符，并且停止读入，贪婪性