Provides means to produce concatenated messages in language-neutral way. Use this for all concatenations that show up to end users.

Takes a set of objects, formats them, then inserts the formatted strings into the pattern at the appropriate places.

Here are some examples of usage: Example 1:

.    UChar *result, *tzID, *str;
.    UChar pattern[100];
.    t_int32 resultLengthOut, resultlength;
.    UCalendar *cal;
.    UDate d1;
.    UDateFormat *def1;
.    UErrorCode status = U_ZERO_ERROR;
.    str=(UChar*)malloc(sizeof(UChar) * (strlen("disturbance in force") +1));
.    u_uastrcpy(str, "disturbance in force");
.    tzID=(UChar*)malloc(sizeof(UChar) * 4);
.    u_uastrcpy(tzID, "PST");
.    cal=ucal_open(tzID, u_strlen(tzID), "en_US", UCAL_TRADITIONAL, &status);
.    ucal_setDateTime(cal, 1999, UCAL_MARCH, 18, 0, 0, 0, &status);
.    d1=ucal_getMillis(cal, &status);
.    u_uastrcpy(pattern, "On {0, date, long}, there was a {1} on planet {2,number,integer}");
.    resultlength=0;
.    resultLengthOut=u_formatMessage( "en_US", pattern, u_strlen(pattern), NULL, resultlength, &status, d1, str, 7);
.    if(status==U_BUFFER_OVERFLOW_ERROR){
.        status=U_ZERO_ERROR;
.        resultlength=resultLengthOut+1;
.        result=(UChar*)realloc(result, sizeof(UChar) * resultlength);
.        u_formatMessage( "en_US", pattern, u_strlen(pattern), result, resultlength, &status, d1, str, 7);
.    }
.    printf("%s\n", austrdup(result) );//austrdup( a function used to convert UChar* to char*)
.    //output>: "On March 18, 1999, there was a disturbance in force on planet 7

Typically, the message format will come from resources, and the arguments will be dynamically set at runtime.

Example 2:

.    UChar* str;
.    UErrorCode status = U_ZERO_ERROR;
.    UChar *result;
.    UChar pattern[100];
.    t_int32 resultlength,resultLengthOut, i;
.    double testArgs= { 100.0, 1.0, 0.0};
.    str=(UChar*)malloc(sizeof(UChar) * 10);
.    u_uastrcpy(str, "MyDisk");
.    u_uastrcpy(pattern, "The disk {1} contains {0,choice,0#no files|1#one file|1<{0,number,integer} files}");
.    for(i=0; i<3; i++){
.      resultlength=0;
.    resultLengthOut=u_formatMessage( "en_US", pattern, u_strlen(pattern), NULL, resultlength, &status, testArgs[i], str);
.    if(status==U_BUFFER_OVERFLOW_ERROR){
.        status=U_ZERO_ERROR;
.        resultlength=resultLengthOut+1;
.        result=(UChar*)malloc(sizeof(UChar) * resultlength);
.        u_formatMessage( "en_US", pattern, u_strlen(pattern), result, resultlength, &status, testArgs[i], str);
.    }
.    printf("%s\n", austrdup(result) );  //austrdup( a function used to convert UChar* to char*)
.    free(result);
.    }
.    // output, with different testArgs:
.    // output: The disk "MyDisk" contains 100 files.
.    // output: The disk "MyDisk" contains one file.
.    // output: The disk "MyDisk" contains no files.

The pattern is of the following form. Legend:

.      {optional item}
.      (group that may be repeated)*

Do not confuse optional items with items inside quotes braces, such as this: "{". Quoted braces are literals.

.      messageFormatPattern := string ( "{" messageFormatElement "}" string )*
.       
.      messageFormatElement := argument { "," elementFormat }
.       
.      elementFormat := "time" { "," datetimeStyle }
.                     | "date" { "," datetimeStyle }
.                     | "number" { "," numberStyle }
.                     | "choice" "," choiceStyle
.  
.      datetimeStyle := "short"
.                     | "medium"
.                     | "long"
.                     | "full"
.                     | dateFormatPattern
.
.      numberStyle :=   "currency"
.                     | "percent"
.                     | "integer"
.                     | numberFormatPattern
. 
.      choiceStyle :=   choiceFormatPattern

If there is no elementFormat, then the argument must be a string, which is substituted. If there is no dateTimeStyle or numberStyle, then the default format is used (e.g. NumberFormat.getInstance(), DateFormat.getDefaultTime() or DateFormat.getDefaultDate(). For a ChoiceFormat, the pattern must always be specified, since there is no default.

In strings, single quotes can be used to quote the "{" sign if necessary. A real single quote is represented by ''. Inside a messageFormatElement, quotes are [not] removed. For example, {1,number,$'#',##} will produce a number format with the pound-sign quoted, with a result such as: "$#31,45".

If a pattern is used, then unquoted braces in the pattern, if any, must match: that is, "ab {0} de" and "ab '}' de" are ok, but "ab {0'}' de" and "ab } de" are not.

The argument is a number from 0 to 9, which corresponds to the arguments presented in an array to be formatted.

It is ok to have unused arguments in the array. With missing arguments or arguments that are not of the right class for the specified format, a failing UErrorCode result is set.

[Note:] As we see above, the string produced by a choice Format in MessageFormat is treated specially; occurances of '{' are used to indicated subformats.

[Note:] Formats are numbered by order of variable in the string. This is [not] the same as the argument numbering!

.   For example: with "abc{2}def{3}ghi{0}...",
.   
.   format0 affects the first variable {2}
.   format1 affects the second variable {3}
.   format2 affects the second variable {0}

and so on.