從字典上比較std::strncmp(函數，對不多於兩個以空值結尾的字符串的字符進行比較，並根據結果返回一個整數。
- 此函數將兩個字符串和一個數字num作為參數，並比較兩個字符串的最大前num個字節。
- 數最多應等於最長字符串的長度。如果將num定義為大於字符串長度，則比較將一直進行到兩個字符串的null-character('\ 0')。
- 此函數按字典順序比較兩個字符串。它從每個字符串的第一個字符開始比較。如果它們彼此相等，則繼續並比較每個字符串的下一個字符，依此類推。
- 比較過程將一直終止，直到到達一個終止字符串null-character或兩個字符串的num個字符都匹配為止。
用法:
int strncmp(const char *str1, const char *str2, size_t count); 參數： str1 and str2: C string to be compared. count:Maximum number of characters to compare. size_t is an unsigned integral type. 返回值： Value Meaning Less than zero str1 is less than str2. Zero str1 is equal to str2. Greater than zero str1 is greater than str2.
如果任一字符串中的字符數少於計數，則在遇到第一個null時比較結束。
What does strcmp() return?
strncmp()函數在比較的基礎上返回三種不同類型的整數值：
1.大於零(> 0)：如果在num字符之前str1和str2的字符不匹配並且str1字符的ASCII值大於str2字符的ASCII值，則返回正值。結果，我們可以說str1在字典上大於str2。
// C, C++ program to demonstrate
// functionality of strncmp()
#include <stdio.h>
#include <string.h>
int main()
{
// Take any two strings
char str1[10] = "aksh";
char str2[10] = "akash";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is:%d", result);
return 0;
}輸出：
str1 is greater than str2 Value returned by strncmp() is:18
2.小於零(<0)：如果str1和str2的字符在num字符之前不匹配並且str1字符的ASCII值小於str2字符的ASCII值，則返回負值。結果，我們可以說str2在字典上大於str1。
// C, C++ program to demonstrate
// functionality of strncmp()
#include <stdio.h>
#include <string.h>
int main()
{
// Take any two strings
char str1[10] = "akash";
char str2[10] = "aksh";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is:%d", result);
return 0;
}輸出：
str2 is greater than str1 Value returned by strncmp() is:-18
3.等於零(0)：如果str1的字符與str2的字符(最多num個字符)匹配，則此函數返回零。結果，我們不能說str1等於str2，直到num等於任一字符串的長度。
// C, C++ program to demonstrate
// functionality of strncmp()
#include <stdio.h>
#include <string.h>
int main()
{
// Take any two strings
char str1[10] = "akash";
char str2[10] = "akas";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is:%d", result);
return 0;
}輸出：
str1 is equal to str2 upto num characters Value returned by strncmp() is:0
注意：當字符串不同時，在兩種情況下，您都會發現strncmp()函數返回的值是str1和str2中第一個不匹配字符的ASCII值之間的差。
More Examples
範例1：
// CPP program to illustrate strncmp()
#include <cstring>
#include <iostream>
void display(char* abc, char* xyz, int res, int count)
{
if (res > 0)
std::cout << xyz << " come-before " << abc;
else if (res < 0)
std::cout << abc << " come-before " << xyz;
else
std::cout << "First " << count << " characters of string "
<< abc << " and " << xyz << " are same";
}
int main()
{
char abc[] = "GeeksforGeeks";
char xyz[] = "Geeks";
int res;
res = std::strncmp(abc, xyz, 4);
display(abc, xyz, res, 4);
return 0;
}輸出：
First 4 characters of string GeeksforGeeks and Geeks are same
範例2：
// CPP program to illustrate strncmp()
#include <cstring>
#include <iostream>
void display(char* abc, char* xyz, int res, int count)
{
if (res > 0)
std::cout << xyz << " come-before " << abc;
else if (res < 0)
std::cout << abc << " come-before " << xyz;
else
std::cout << "First " << count << " characters of string " <<
abc << " and " << xyz << " are same";
;
}
int main()
{
char abc[] = "GeeksforGeeks";
char xyz[] = "Geeks";
int res;
res = std::strncmp(abc, xyz, 6);
display(abc, xyz, res, 6);
return 0;
}輸出：
Geeks come-before GeeksforGeeks
相關用法
注：本文由純淨天空篩選整理自 std::strncmp() in C++。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。