经典编程900例（c语言）（第二十八篇）

例342：字符串大小转换函数strlwr()和strupr()

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    // strlwr将字符串中的S参数转换为小写形式
    // strupr将字符串中的S参数转换为大写形式
    // strlwr和strupr不是标准C库函数，只能在VC中使用。linux gcc环境下需要自行定义这个函数
    printf(strlwr("1001 C/C++ Tips!\n"));
    printf(strupr("1001 C/C++ Tips!\n"));
    return 0;
}

例343：字符串连接函数strcat()

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    char name[64] = "Triggerhill's I'm so";

    strcat(name, " Happy");
    printf("Happy's full name is %s\n", name);  // Happy's full name is Triggerhill's I'm so Happy
    return 0;
}

例344：字符串中查找字符函数strchr()

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    char title[64] = "1001 C/C++ Tips!";
    char *ptr;

    // strchr在参数str所指向的字符串中搜索第一次出现字符c（一个无符号字符）的指针
    if (ptr = strchr(title, 'C'))
        printf("First occurrence of C is at offset %d\n", ptr - title);// First occurrence of C is at offset 5
    else
        printf("Character not found\n");
    return 0;
}

例345：字符串比较函数strcmp()

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    printf("Comparing Abc with Abc %d\n", strcmp("Abc", "Abc"));    // Comparing Abc with Abc 0
    printf("Comparing abc with Abc %d\n", strcmp("abc", "Abc"));    // Comparing abc with Abc 1
    printf("Comparing abcd with abc %d\n", strcmp("abcd", "abc"));  // Comparing abcd with abc 1
    printf("Comparing Abc with Abcd %d\n", strcmp("Abc", "Abcd"));  // Comparing Abc with Abcd -1
    return 0;
}

例346：字符串复制函数strcpy()

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    char title[] = "Jamsa's 1001 C/C++ Tips";
    char book[128];

    strcpy(book, title);
    printf("Book name %s\n", book);	// Book name Jamsa's 1001 C/C++ Tips
    return 0;
}

例347：字符串复制函数strdup()

#include <stdio.h>
#include <string.h>
 
int main(int argc, char const *argv[])
{
    char *title;

    // strdup将串拷贝到新建的位置处, 内部使用malloc(), 不用时要用free 
    if ((title = strdup("Jamsa's 1001 C/C++ Tips")))
        printf("Title: %s\n", title);
    else 
        printf("Error duplicating string");
    return 0;
}

例348：自定义函数比较两个字符串是否相等

#include <stdio.h>

/**
 * 比较两个字符串是否相等
 * 相等返回1, 否则返回0
 */
int streql(char *str1, char *str2)
{
    while ((*str1 == *str2) && (*str1))
    {
        str1++;
        str2++;
    }

    return((*str1 == NULL) && (*str2 == NULL));
}

int main(int argc, char const *argv[])
{
    printf("Testing Abc and Abc %d\n", streql("Abc", "Abc"));   // Testing Abc and Abc 1
    printf("Testing abc and Abc %d\n", streql("abc", "Abc"));   // Testing abc and Abc 0
    printf("Testing abcd and abc %d\n", streql("abcd", "abc")); // Testing abcd and abc 0
    return 0;
}

例349：自定义函数比较两个字符串是否相等（不区分大小写）

#include <stdio.h>
#include <ctype.h>

/**
 * 不区分大小写比较字符串是否相等
 */
int strieql(char *str1, char *str2)
{
    while ((toupper(*str1) == toupper(*str2)) && (*str1))
    {
        str1++;
        str2++;
    }

    return((*str1 == NULL) && (*str2 == NULL));
}

int main(int argc, char const *argv[])
{
    printf("Testing Abc and Abc %d\n", strieql("Abc", "Abc"));      // Testing Abc and Abc 1
    printf("Testing abc and Abc %d\n", strieql("abc", "Abc"));      // Testing abc and Abc 1
    printf("Testing abcd and abc %d\n", strieql("abcd", "abc"));    // Testing abcd and abc 0
    return 0;
}

例350：自定义函数查找字符串中的字符下标

#include <stdio.h>

/**
 * 返回字符串中指定字符的下标, 没有就返回'\0'的下标, 即字符串的长度
 */
int str_index(const char *string, int letter)
{
    char *original = (char *)string;

    while ((*string != letter) && (*string))
        string++;

    return(string - original);
}

int main(int argc, char const *argv[])
{
    printf("Location of C is %d\n", str_index("1001 C/C++", 'C'));// Location of C is 5
    printf("Location of x is %d\n", str_index("1001 C/C++", 'x'));// Location of x is 10
    return 0;
}

例351：字符串长度函数strlen()

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    char book_title[] = "Jamsa's 1001 C/C++ Tips";

    printf("%s contains %d characters\n", book_title, strlen(book_title));// Jamsa's 1001 C/C++ Tips contains 23 characters
    return 0;
}

例352：字符串连接函数strncat()

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    char name[64] = "Bill";

    // char * strncat(char *dest, const char *src, size_t n);
    // 在dest的结尾追加src的前n个字符
    strncat(name, " and Hillary", 4);
    printf("Did you vote for %s?\n", name); // Did you vote for Bill and?

    return 0;
}